AC
Abbreviation with 16 meanings
| Stands for | Alternating current |
|---|---|
| Meanings | 16 |
| Categories | Science & Engineering, Units & Measurements, Transportation & Travel, Medical, Law & Legal, Texting & Internet Slang, Military, Religion, Geography & Places, Business & Finance |
| Also written | Ac, ac |
AC has 16 meanings. The most common are Alternating current (electronics & electrical) and Acre (US customary and imperial unit); it can also stand for Air Canada, Ante cibum (before meals), Acromioclavicular (joint), Anterior chamber (of the eye) and Assist-control ventilation, plus 9 more listed below.
Meanings of AC at a glance
| # | AC stands for | Context |
|---|---|---|
| 1 | Alternating current | Science & Engineering › Electronics & Electrical |
| 2 | Acre | Units & Measurements › US Customary and Imperial Unit |
| 3 | Air Canada | Transportation & Travel › Airline Code |
| 4 | Ante cibum (before meals) | Medical › Prescription |
| 5 | Acromioclavicular (joint) | Medical › Anatomy |
| 6 | Anterior chamber (of the eye) | Medical › Anatomy |
| 7 | Assist-control ventilation | Medical › Respiratory |
| 8 | Acetyl group | Science & Engineering › Chemistry |
| 9 | Appeal Cases | Law & Legal › Legal Citation |
| 10 | Armor Class | Texting & Internet Slang › Gaming Slang |
| 11 | Air Traffic Controller (US Navy rating) | Military › US Navy and Coast Guard Rating |
| 12 | Aircraftman | Military › British Military Rank |
| 13 | Acts of the Apostles | Religion › Bible Book |
| 14 | Ascension Island | Geography & Places › Country Code |
| 15 | Actinium | Science & Engineering › Chemical Element |
| 16 | Actual cost | Business & Finance › Project Management |
1. Alternating current
Science & Engineering · Electronics & Electrical Abbreviations
Electric current that reverses direction many times a second, following a sine wave, the form delivered by power grids to homes and businesses. North America uses 60 hertz, with household outlets at about 120 volts, while most of the world uses 50 hertz at 220-240 volts.
Example: The adapter converts 100-240 V AC from the wall into 20 V DC for the laptop.
AC won the "War of the Currents" of the late 1880s and 1890s, in which Thomas Edison promoted direct current while George Westinghouse backed AC systems using Nikola Tesla's induction motor patents. Transformers can step AC voltage up for efficient long-distance transmission and down for safe use, which DC could not easily do at the time. Westinghouse lit the 1893 Chicago World's Fair with AC, and the Niagara Falls power plant of 1895-1896 sealed its victory. Japan still runs at 50 Hz in the east and 60 Hz in the west.
2. Acre (ac)
Units & Measurements · US Customary and Imperial Unit Abbreviations
A land area of 43,560 square feet, about 4,047 square meters or 0.405 hectare. Farms, house lots, parks and wildfires are measured in acres in the United States, the UK and several other countries.
Example: Wooded building lot, 2.5 ac, with road frontage and electric at the street.
Historically an acre was the area a team of oxen could plow in a day, standardized as one furlong by one chain. An American football field including the end zones covers about 1.32 acres. There are 640 acres in a square mile; a hectare is about 2.47 acres.
3. Air Canada
Transportation & Travel · Airline Code Abbreviations
Canada's flag carrier and largest airline, headquartered in Montreal with its largest hub at Toronto Pearson. Air Canada co-founded Star Alliance in 1997.
Example: AC 849 from Toronto to London Heathrow departs at 9:30 p.m.
ICAO code ACA; callsign "Air Canada." Founded in 1937 as Trans-Canada Air Lines and renamed in 1965. It absorbed Canadian Airlines International in 2000. Its subsidiaries include Air Canada Rouge for leisure routes and Air Canada Express regional flights. The letters AC also commonly mean air conditioning.
4. Ante cibum (before meals)
Medical · Prescription Abbreviations
Timing instruction to take a drug or perform a test before eating, usually about 30 minutes before a meal. It is used for drugs whose absorption food reduces and for fingerstick blood glucose checks done before each meal in patients on insulin.
Example: Pantoprazole 40 mg PO daily AC breakfast; fingerstick glucose AC and HS.
Latin "ante cibum", "before food". Also written a.c. or ac. Levothyroxine, alendronate and many proton pump inhibitors are classic AC drugs; alendronate specifically requires at least 30 minutes before the first food, drink or other medicine of the day. In printed labels, pharmacists usually translate AC into "before meals" or "on an empty stomach".
5. Acromioclavicular (joint)
Medical · Anatomy Abbreviations
Small joint at the top of the shoulder where the outer end of the clavicle meets the acromion of the scapula. AC separations, the "separated shoulder", commonly follow falls directly onto the shoulder in hockey, rugby, football and cycling.
Example: Type III AC separation after going over the handlebars; sling and rehab.
Injuries are graded on the Rockwood scale from type I to VI according to ligament damage and displacement, and types I and II are treated without surgery. AC joint arthritis is a frequent cause of top-of-shoulder pain in weightlifters. A separated shoulder differs from a dislocated shoulder, which involves the glenohumeral joint.
6. Anterior chamber (of the eye)
Medical · Anatomy Abbreviations
Fluid-filled space between the cornea and the iris, containing aqueous humor. Eye examinations record whether the anterior chamber is deep and quiet; cells and flare indicate inflammation (uveitis), and blood layered in the chamber is a hyphema.
Example: Slit lamp: AC 2+ cell and flare; anterior uveitis, starting steroid drops.
Ophthalmology notes often write "AC D&Q" for deep and quiet. A shallow anterior chamber raises the risk of angle-closure glaucoma, which some patients prevent with laser iridotomy. In orthopedics AC means acromioclavicular.
7. Assist-control ventilation
Medical · Respiratory Abbreviations
Mechanical ventilation mode in which the ventilator delivers a full set breath, either a set volume or set pressure, every time the patient triggers a breath, plus mandatory breaths at a minimum backup rate. It is the most common initial mode in intensive care units.
Example: Vent: AC/VC 450 x 16, PEEP 8, FiO2 0.5; patient overbreathing at 28.
Because every triggered breath is fully supported, a patient breathing rapidly can develop respiratory alkalosis or air trapping (breath stacking). Settings are written in order, such as mode, tidal volume, rate, PEEP and FiO2. Versions include volume control (AC/VC) and pressure control (AC/PC). On prescriptions AC means before meals (ante cibum).
8. Acetyl group (Ac)
Science & Engineering · Chemistry Abbreviations
Organic abbreviation for the acetyl group, CH3CO-, found in shorthand such as AcOH (acetic acid), Ac2O (acetic anhydride) and OAc (acetate). Acetylation, the attachment of an acetyl group, turns salicylic acid into aspirin and morphine into heroin.
Example: The alcohol was protected as its OAc ester using Ac2O and pyridine.
As an element symbol Ac means actinium, element 89, but in organic structures it virtually always means acetyl. AcOH and HOAc are both used for acetic acid. In biology, acetylation of histone proteins helps switch genes on, and acetyl-CoA is a central metabolite.
9. Appeal Cases
Law & Legal · Legal Citation Abbreviations
Series of the Law Reports published by the Incorporated Council of Law Reporting for England and Wales, covering decisions of the UK Supreme Court, the former House of Lords and the Privy Council. Citations put the year in square brackets, as in [1932] AC 562 for Donoghue v Stevenson.
Example: Every first-year tort course starts with Donoghue v Stevenson [1932] AC 562.
The Law Reports, begun in 1865, are the most authoritative English reports and should be cited in preference to others when a case appears in them. From 1875 to 1890 the series was cited "App Cas". Square brackets mean the year is needed to find the volume; round brackets mean the volume number alone suffices. UK style omits full stops.
10. Armor Class
Texting & Internet Slang · Gaming Slang Abbreviations
Number representing how hard a character is to hit in Dungeons & Dragons and other d20 games; an attack roll must meet or beat it to land.
Example: My wizard has 12 AC, so please keep the goblins away from me.
In older editions such as AD&D, lower AC was better and was paired with the THAC0 system, while third edition (2000) introduced the modern rule that higher is better. Shields, armor and spells raise AC. Outside games, AC usually means air conditioning or alternating current.
11. Air Traffic Controller (US Navy rating)
Military · US Navy and Coast Guard Rating Abbreviations
Sailors in this rating control aircraft at naval air stations and in the air traffic control centers of carriers and amphibious assault ships, handling departures, approaches and recoveries in all weather. Training leads to Federal Aviation Administration certification.
Example: AC1 Romero worked the carrier approach frequency during the night recovery.
Navy controllers learn their trade at the Naval Air Technical Training Center in Pensacola, Florida. Their certifications can carry over to civilian air traffic control careers. Within the military category, AC can also mean active component, and in Britain the RAF uses AC for Aircraftman.
12. Aircraftman
Military · British Military Rank Abbreviations
Lowest rank in the Royal Air Force, held by recruits during and immediately after basic training; women hold the title Aircraftwoman. Aircraftmen progress to leading aircraftman on completing trade training.
Example: AC Rowe passed out of basic training at RAF Halton last week.
RAF recruit training takes place at RAF Halton in Buckinghamshire. The title dates from the RAF's formation in 1918. In other contexts, AC means air conditioning or alternating current, and in the US Navy it is the air traffic controller rating.
13. Acts of the Apostles (Ac)
Religion · Bible Book Abbreviations
Fifth book of the New Testament, 28 chapters, continuing Luke's Gospel with the coming of the Holy Spirit at Pentecost (chapter 2), the growth of the early church in Jerusalem and Paul's conversion and missionary journeys, ending with Paul under house arrest in Rome.
Example: Paul's conversion on the road to Damascus is described in Ac 9.
SBL and Chicago leave Acts unabbreviated, while the New Jerusalem Bible and some reference works use Ac. The book is the main historical source for the first decades of Christianity. Its "we passages" suggest the author traveled with Paul.
14. Ascension Island
Geography & Places · Country Code Abbreviations
Exceptionally reserved ISO code for Ascension Island, part of the British territory of Saint Helena, Ascension and Tristan da Cunha. The .ac domain is open to registrants worldwide and popular with academic and tech projects.
Example: The .ac domain of AC is different from .ac.uk, which marks British universities.
Ascension has no permanent population; residents are contract workers. Its airfield, Wideawake, is used by the UK and US militaries.
15. Actinium (Ac)
Science & Engineering · Chemical Element Abbreviations
Actinium (element 89) gives its name to the actinide series of 15 elements from actinium to lawrencium. So radioactive that it glows pale blue in the dark, it is rare and mostly of research interest, though actinium-225 is a promising source of alpha particles for targeted cancer therapy.
Example: Supplies of Ac-225 for clinical trials have come largely from aging stocks of thorium-229.
André-Louis Debierne reported actinium in 1899 from pitchblende residues left by the Curies, though historians debate whether Friedrich Oskar Giesel, who described it independently in 1902, deserves the credit. The name comes from Greek aktis (ray, beam). In organic chemistry, Ac is also the standard abbreviation for the acetyl group, as in AcOH for acetic acid.
16. Actual cost
Business & Finance · Project Management Abbreviations
Total cost actually incurred for the work performed during a period, compared with earned value to assess cost efficiency.
Example: AC to date is $240,000 against $200,000 of earned value.
Also called ACWP (actual cost of work performed). Labor, materials and overhead must be recorded on the same basis as the budget for comparisons to be valid.
Related abbreviations
More electronics & electrical abbreviations
- ADC – Analog-to-digital converter
- AFCI – Arc-fault circuit interrupter
- AM – Amplitude modulation
- AMOLED – Active-matrix organic light-emitting diode
- ASIC – Application-specific integrated circuit
- AWG – American wire gauge
- BGA – Ball grid array
- BJT – Bipolar junction transistor
See all 82 electronics & electrical abbreviations →
More US customary and imperial unit abbreviations
- ac-ft – Acre-foot
- bbl – Barrel (oil)
- bd ft – Board foot
- bu – Bushel
- CCF – Hundred cubic feet
- ch – Chain
- cu ft – Cubic foot
- cu in – Cubic inch
See all 43 US customary and imperial unit abbreviations →
This entry is for general education and is not medical or legal advice. Abbreviation use varies between institutions; always confirm in context.