World English Dictionary
a or A (eɪ)
n , pl a's, A's, As
1.  the first letter and first vowel of the modern English alphabet
2.  any of several speech sounds represented by this letter, in English as in take, bag, calm, shortage, or cobra
3.  Also called: alpha the first in a series, esp the highest grade or mark, as in an examination
4.  from A to Z from start to finish, thoroughly and in detail
A or A

a1 (ə, (stressed or emphatic) eɪ)
determiner (indefinite article; used before an initial consonant) (preceded by once, twice, several times, etc)
1.  used preceding a singular countable noun, if the noun is not previously specified or known: a dog; a terrible disappointment
2.  used preceding a proper noun to indicate that a person or thing has some of the qualities of the one named: a Romeo; a Shylock
3.  used preceding a noun or determiner of quantity: a cupful; a dozen eggs; a great many; to read a lot
4.  used preceding a noun indicating a concrete or abstract thing capable of being divided: half a loaf; a quarter of a minute
5.  each or every; per: once a day; fifty pence a pound
6.  a certain; one: to change policy at a stroke; a Mr Jones called
7.  (preceded by not) any at all: not a hope

a2 (ə)
an informal or dialect word for have : they'd a said if they'd known

a3 (ə)
(usually linked to the preceding noun) an informal form of of : sorta sad; a kinda waste

symbol for
1.  acceleration
2.  are(s) (metric measure of land)
3.  atto-
4.  chess See algebraic notation

symbol for
1.  music
 a.  a note having a frequency of 440 hertz (A above middle C) or this value multiplied or divided by any power of 2; the sixth note of the scale of C major
 b.  a key, string, or pipe producing this note
 c.  the major or minor key having this note as its tonic
2.  a human blood type of the ABO group, containing the A antigen
3.  (in Britain) a major arterial road: the A3 runs from London to Portsmouth
4.  formerly, in Britain
 a.  a film certified for viewing by anyone, but which contains material that some parents may not wish their children to see
 b.  (as modifier): an A film
5.  mass number
6.  the number 10 in hexadecimal notation
7.  cards ace
8.  chem argon (now superseded by Ar)
9.  ampere(s)
10.  Also: at ampere-turn
11.  absolute (temperature)
12.  (in circuit diagrams) ammeter
13.  area
14.  (in combination) atomic: an A-bomb; an A-plant
15.  chem affinity
16.  biochem adenine
17.  logic E I Compare O a universal affirmative categorical proposition, such as all men are mortal: often symbolized as SaP
18.  a.  a person whose job is in top management, or who holds a senior administrative or professional position
 b.  See also occupation groupings (as modifier): an A worker
abbreviation for
19.  Austria (international car registration)
[from Latin a(ffirmo) I affirm]

symbol for
angstrom unit

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

indefinite article, c.1150, a variation of O.E. an (see an) in which the -n- began to disappear before consonants, a process mostly complete by mid-14c. The -n- also was retained before words beginning with a sounded -h- until c.1600; it still is retained by many writers before
unaccented syllables in h- or (e)u-, but is now no longer normally spoken as such. The -n- also lingered (especially in southern England dialect) before -w- and -y- through 15c.

as in twice a day, etc., from O.E. an "on," in this case "on each." The sense was extended from time to measure, price, place, etc. The habit of tacking a onto a gerund (as in a-hunting we will go) died out 18c.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

a abbr.

  1. area

  2. asymmetrical

  3. specific absorption coefficient (often italic)

  4. systemic arterial blood (used as a subscript)

  5. total acidity

A abbr.

  1. absorbance (often italic)

  2. alveolar gas (used as a subscript)

  3. adenine

  4. ammeter

  5. AMP (in polynucleotides)

  6. ampere

  7. angstrom

  8. area

Å abbr.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
Abbreviation of adenine, ampere, angstrom, area
Abbreviation of angstrom
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Abbreviations & Acronyms
  1. accusative

  2. ace

  3. across

  4. adenine

  5. alto

  6. American Stock Exchange

  7. ammeter

  8. ampere

  9. angstrom

  10. area

  11. Asian (as in personal ads)

  12. Baseball assist

  13. Austria (international vehicle ID)

The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Bible Dictionary

A definition

Alpha, the first letter of the Greek alphabet, as Omega is the last. These letters occur in the text of Rev. 1:8,11; 21:6; 22:13, and are represented by "Alpha" and "Omega" respectively (omitted in R.V., 1:11). They mean "the first and last." (Comp. Heb. 12:2; Isa. 41:4; 44:6; Rev. 1:11,17; 2:8.) In the symbols of the early Christian Church these two letters are frequently combined with the cross or with Christ's monogram to denote his divinity.

Easton's 1897 Bible Dictionary
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