A (disambiguation)
A is the first letter of the Latin and English alphabet.
Look up A in Wiktionary, the free dictionary.
A may also refer to:
Science and technology
Quantities and units
- a, a measure for the attraction between particles in the Van der Waals equation
- A value, a measure of substituent effects on the stereochemistry of cyclohexane
- absorbance (A)
- acceleration (a)
- activity (chemistry) (a)
- adsorption (a)
- annum (a), for year
- are (a), a unit of area (equal to 100 square metres; redirects to hectare)
- atto- (a-), the SI prefix meaning 10−18
- Ampere (A), unit of electric current
- ångström (Å) a unit of length (equal to 1×10−10 metres)
- area (A)
- attenuation coefficient (a)
- Bohr radius (a0)
- chemical affinity (A)
- gain (electronics) (A)
- Hall coefficient (AH)
- Hamaker constant (A)
- Helmholtz free energy (A)
- Hyperfine coupling constant (a or A)
- magnetic vector potential (A)
- mass number of a nuclide (A)
- pre-exponential factor (A)
- one of the reciprocal lattice vectors (a*)
- relative atomic mass (Ar)
- Richardson's constant (A)
- rotational constant (A)
- specific surface area (a)
- thermal diffusivity (a)
- unit cell length (a)
Astronomy
- A whitish-blue class of stars in the Morgan–Keenan system; see Stellar classification
- Part of the provisional designation of a comet (e.g., C/1760 A1), indicating a January 1 through 15 discovery
- The semi-major axis of an orbit
Biology
- A+ and A−, human blood types
- Vitamin A, also called retinol, an essential human nutrient
- Haplogroup A (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
- Haplogroup A (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
- Adenine, a nucleic acid
- Adenosine, a nucleoside
- A (or Ala), abbreviation for amino acid alanine
- ATC code A, Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System
Programming languages
- A+ (programming language)
- A♯, an object-oriented functional programming language
- A Sharp (.NET) (also written "A#"), a port of Ada to the Microsoft .NET Platform
- BASIC A+
Other uses in computing
- A* search algorithm, a pathfinding algorithm
- A-0 System, an early computer compiler
<a></a>, the HTML element for an anchor tag- a, equivalent (qname) to the RDF Schema Property rdf:type
- A level of web accessibility defined by the Web Content Accessibility Guidelines
- The address record type of DNS, defined in RFC 1035
Mathematics and logic
- A numerical digit meaning ten in hexadecimal and other positional numeral systems with a radix of 11 or greater
- Sometimes in blackboard bold represents the algebraic numbers () (U+1D538 in Unicode)
- Universal quantifier in symbolic logic (symbol ∀ or , an inverted letter A)
- Universal affirmative, one of the four types of categorical proposition in logic
- Mills' constant is represented by the symbol A
- Glaisher–Kinkelin constant is also often represented by the symbol A
Other uses in science and technology
- A battery, a vacuum tube filament type battery
- A battery (size), a standard battery size
- Anode, an electrode
- A, historical symbol for chemical element argon, currently Ar
- The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics
Arts and media
Books
- "A", a poem by twentieth century author Louis Zukofsky
- a, A Novel, by twentieth century artist Andy Warhol
- A, the name of the Fourth Raikage, the leader of Kumogakure in the Naruto manga series
- A (Pretty Little Liars), the main antagonist in the Pretty Little Liars book and TV series
- A (for "adultery"), the titular letter in the novel The Scarlet Letter
- "A" Is for Alibi, the first novel in Sue Grafton's "Alphabet mystery" series, published in 1982
- Matthew Arnold, who used the pseudonym "A"
- Isaac Asimov, who used the pseudonym "Dr. A"
- Alexander Pope, who used the pseudonym "A"
Films
- A (1965 film), a short film animated by Jan Lenica
- A (1998 Kannada film), an Indian movie directed by Upendra
- A (1998 Japanese film), a documentary film about a Buddhist sect called "A"
- A (2002 film), a British documentary film
Film ratings
- A, a rating in India's Central Board of Film Certification
- A certificate, a film rating used by the Canadian motion picture rating system
- A, a British Board of Film Classification rating used from 1912 to 1982, see History of British film certificates
Television
- CTV 2, a Canadian television system formerly known as A-Channel and A
- A, the main antagonist and unknown character of the show Pretty Little Liars
- "A" (The Walking Dead), an episode of the television series The Walking Dead
- A, code name of Ange, the main protagonist of the anime show Princess Principal
- "A"-logo for the Spanish network Antena 3.
- A, the production code for the 1963 Doctor Who serial An Unearthly Child
Music
- A (musical note), the sixth solfège note
- A major, a scale
- A minor, a scale
- A major chord; see Chord names and symbols (popular music)
Performers
- A (band), a British alternative rock band
Albums
- A (Agnetha Fältskog album), 2013
- A (Cass McCombs album), 2003
- A (Jimmy Raney album), 1957
- A (Jethro Tull album), 1980
- A (Usher and Zaytoven album), 2018
- A, a Denki Groove album (read as "Ace")
- A (Ayumi Hamasaki EP), 1999
- A (single album), a 2015 single by the Korean band Big Bang
- A!, Alexa Feser 2019
- A' (album), an album by Afrirampo
Songs
- A or Side A, the top or first side of a gramophone record
- "A" (Rainbow song), a 2010 single by Rainbow
- "A", song by A from 'A' vs. Monkey Kong
- "A", song by Got7 from Got Love (2014)
- "A", song by the band Barenaked Ladies from Maybe You Should Drive
- "A", song by Cartel from Chroma
- "A", a song in the Dance Dance Revolution video game series, by DJ Amuro
Other media
/a/, the anime and manga section on 4chan- A, a Japanese video game rating in the Computer Entertainment Rating Organization suitable for all ages.
Geography
- Austria, on the vehicle registration plates of the European Union
- "The A", a nickname for the U.S. city of Atlanta, Georgia
Linguistics
Letters
- A (or a), the first letter of the Latin alphabet
- A (Bengali), the romanized name of the Bengali letter অ
- A (cuneiform), the romanized name of a cuneiform sign
- A (Cyrillic) (A or а), the first letter of the Cyrillic alphabet
- A (kana) (or a), the romanized name of the Hiragana syllable letter あ and of the Katakana syllable letter ア used in Japanese, which may also be used to represent Asia
- Alpha (Α or α), the first letter of the Greek alphabet
Other uses in linguistics
- A and an, the indefinite article in English
- A, a glossing abbreviation for agent-like argument of canonical transitive verb
- a, the IPA representation of the open front unrounded vowel
- ɑ, the IPA representation of the open back unrounded vowel
- a., an abbreviation of ante (Latin for "before") used in etymologies
People
- A (pharaoh), an Egyptian pharaoh
- A Martinez, an American actor and singer
- Matthew Arnold, who used the pseudonym "A"
- Isaac Asimov, who used the pseudonym "Dr. A"
- Alexander Pope, who used the pseudonym "A"
- Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116, a Swedish child born in 1991, alternately called "A"
Philosophy and religion
- A, the Dominical letter of a common year starting on Sunday
- Scarlet A, symbol for atheism adopted by the Out Campaign, a public awareness initiated by Elizabeth Cornwell and Richard Dawkins
- Alpha, (sometimes A) in Christian theology, a metaphor for the beginning/creation of time and matter
- An anarchist symbol, an A within a circle
Transport
Automobile
- Ford Model A, a name used by two separate cars produced by the Ford Motor Company:
- Geometry A, an electric mid-size sedan by Geely Auto
Rail
- A (S-train) a service on the S-train network in Copenhagen
- Line A of the Buenos Aires Subte
- Line A (Prague Metro)
- Mexico City Metro Line A
- NZR A class (disambiguation) two New Zealand steam locomotive classes
- RER A, a line in the RER of Paris
- Lyon Metro Line A
- Toei Asakusa Line, a subway service operated by the Tokyo Metropolitan Bureau of Transportation (Toei), labeled
- The official West Japan Railway Company service symbol for:
- United States
- A (Los Angeles Railway)
- A (New York City Subway service), also known as the "A Eighth Avenue Express"
- Alton Railroad (reporting mark)
- A Line (Los Angeles Metro)
- Britain
- LCDR A class, British 0-4-4T steam locomotives introduced in 1875
- LD&ECR Class A, British 0-6-2T steam locomotives introduced in 1895
- LNWR Class A, British 0-8-0 steam locomotives introduced in 1893
- NER Class A, British 2-4-2T steam locomotives introduced in 1886
- SER A class, British 4-4-0 steam locomotives introduced in 1879
- Taff Vale Railway A class, British 0-6-2T steam locomotives introduced in 1914
Ships
- A (motor yacht) (M/Y A), a 119m yacht owned by Andrey Melnichenko
- A (sailing yacht) (S/Y A), a 143m yacht owned by Andrey Melnichenko
- SMS A, a Kaiserliche Marine tanker
Other uses
- A (grade), an academic grade
- A series of paper sizes defined by ISO 216, e.g. A4, A5 sizes
- A formation, an American football offensive formation
- A-Frame, a type of structure
- Ace, a playing card
- Agilent Technologies, with U.S. ticker symbol A
- Sentinel Peak (Arizona), more commonly known as "A" Mountain for the human-made rock formation in the shape of the letter
- Alfa, the military time zone code for UTC+01:00
- Farmall A, a tractor produced by International Harvester from 1939 to 1947
See also
- Å (disambiguation)
- ⓐ and Ⓐ, see Enclosed Alphanumerics
- Class A (disambiguation)
- Model A (disambiguation)
- Circled a (disambiguation)
- Single-A, or Class A, a classification of minor league baseball
- A band (disambiguation)
- A class (disambiguation)
- A type (disambiguation)
- Aleph (disambiguation)
- Alpha (disambiguation)
- A1 (disambiguation)
- AA (disambiguation)
- AAA (disambiguation)
- AAAA (disambiguation)
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