The first letter of the English and of many other alphabets. The capital A of the alphabets of Middle and Western Europe, as also the small letter (a), besides the forms in Italic, black letter, etc., are all descended from the old Latin A, which was borrowed from the Greek Alpha, of the same form; and this was made from the first letter (&unr_;) of the Phœnician alphabet, the equivalent of the Hebrew Aleph, and itself from the Egyptian origin. The Aleph was a consonant letter, with a guttural breath sound that was not an element of Greek articulation; and the Greeks took it to represent their vowel Alpha with the ä sound, the Phœnician alphabet having no vowel symbols. [ 1913 Webster ]

This letter, in English, is used for several different vowel sounds. See Guide to pronunciation, §§ 43-74. The regular long a, as in fate, etc., is a comparatively modern sound, and has taken the place of what, till about the early part of the 17th century, was a sound of the quality of ä (as in far). [ 1913 Webster ]

2. (Mus.) The name of the sixth tone in the model major scale (that in C), or the first tone of the minor scale, which is named after it the scale in A minor. The second string of the violin is tuned to the A in the treble staff. -- A sharp (A♯) is the name of a musical tone intermediate between A and B. -- A flat (A♭) is the name of a tone intermediate between A and G. [ 1913 Webster ]

A per se (L. per se by itself), one preëminent; a nonesuch. [ Obs. ] [ 1913 Webster ]

O fair Creseide, the flower and A per se
Of Troy and Greece. Chaucer. [ 1913 Webster ]

1. [ Shortened form of an. AS. ān one. See One. ] An adjective, commonly called the indefinite article, and signifying one or any, but less emphatically. “At a birth”; “In a word”; “At a blow”. Shak. It is placed before nouns of the singular number denoting an individual object, or a quality individualized, before collective nouns, and also before plural nouns when the adjective few or the phrase great many or good many is interposed; as, a dog, a house, a man; a color; a sweetness; a hundred, a fleet, a regiment; a few persons, a great many days. It is used for an, for the sake of euphony, before words beginning with a consonant sound [ for exception of certain words beginning with h, see An ]; as, a table, a woman, a year, a unit, a eulogy, a ewe, a oneness, such a one, etc. Formally an was used both before vowels and consonants. [ 1913 Webster ]

2. [ Originally the preposition a (an, on). ] In each; to or for each; as, “twenty leagues a day”, “a hundred pounds a year”, “a dollar a yard”, etc. [ 1913 Webster ]

prep. [ Abbreviated form of an (AS. on). See On. ] 1. In; on; at; by. [ Obs. ] “A God's name.” “Torn a pieces.” “Stand a tiptoe.” “A Sundays” Shak. “Wit that men have now a days.” Chaucer. “Set them a work.” Robynson (More's Utopia). [ 1913 Webster ]

2. In process of; in the act of; into; to; -- used with verbal substantives in -ing which begin with a consonant. This is a shortened form of the preposition an (which was used before the vowel sound); as in a hunting, a building, a begging. “Jacob, when he was a dying” Heb. xi. 21. “We'll a birding together.” “ It was a doing.” Shak. “He burst out a laughing.” Macaulay. The hyphen may be used to connect a with the verbal substantive (as, a-hunting, a-building) or the words may be written separately. This form of expression is now for the most part obsolete, the a being omitted and the verbal substantive treated as a participle. [ 1913 Webster ]

. [ From AS. of off, from. See Of. ] Of. [ Obs. ] “The name of John a Gaunt.” “What time a day is it ?” Shak. “It's six a clock.” B. Jonson. [ 1913 Webster ]

. A barbarous corruption of have, of he, and sometimes of it and of they. “So would I a done” “A brushes his hat.” Shak. [ 1913 Webster ]

. An expletive, void of sense, to fill up the meter [ 1913 Webster ]

A merry heart goes all the day,
Your sad tires in a mile-a. Shak. [ 1913 Webster ]

. A, as a prefix to English words, is derived from various sources. (1) It frequently signifies on or in (from an, a forms of AS. on), denoting a state, as in afoot, on foot, abed, amiss, asleep, aground, aloft, away (AS. onweg), and analogically, ablaze, atremble, etc. (2) AS. of off, from, as in adown (AS. ofdūne off the dun or hill). (3) AS. ā- (Goth. us-, ur-, Ger. er-), usually giving an intensive force, and sometimes the sense of away, on, back, as in arise, abide, ago. (4) Old English y- or i- (corrupted from the AS. inseparable particle ge-, cognate with OHG. ga-, gi-, Goth. ga-), which, as a prefix, made no essential addition to the meaning, as in aware. (5) French à (L. ad to), as in abase, achieve. (6) L. a, ab, abs, from, as in avert. (7) Greek insep. prefix α without, or privative, not, as in abyss, atheist; akin to E. un-. [ 1913 Webster ]

Besides these, there are other sources from which the prefix a takes its origin. [ 1913 Webster ]

A registry mark given by underwriters (as at Lloyd's) to ships in first-class condition. Inferior grades are indicated by A 2 and A 3. [ 1913 Webster ]

A 1 is also applied colloquially to other things to imply superiority; prime; first-class; first-rate. [ 1913 Webster ]

n. 1. acronym for Associate in Arts, a college degree granted for successful completion of a two-year course of study in arts or general topics.
Syn. -- Associate in Arts [ WordNet 1.5 ]

2. Alcoholics Anonymous. [ Acronym. ] [ WordNet 1.5 ]

n. 1. the American Association for the Advancement of Science, an organization with headquarters in Washington, D.C. Its goal is to advance the physical and social sciences, and it publishes a weekly journal Science, with original research articles as well as reviews and commentary. [ Acronym. ]
Syn. -- American Association for the Advancement of Science. [ WordNet 1.5 ]