a-

{{11}}a- (1) in native (derived from Old English) words, it most commonly represents O.E. an "on" (see A (Cf. a) (2)), as in alive, asleep, abroad, afoot, etc., forming adjectives and adverbs from nouns; but it also can be Middle English of, as in anew, abreast (1590s); or a reduced form of Old English past participle prefix ge-, as in aware; or the Old English intensive a-, as in arise, awake, ashame, marking a verb as momentary, a single event. In words from Romanic languages, often it represents L. ad- "to, at."

t naturally happened that all these [i]a- prefixes were at length confusedly lumped together in idea, and the resultant a- looked upon as vaguely intensive, rhetorical, euphonic, or even archaic, and wholly otiose. [OED]

{{12}}a- (2) prefix meaning "not," from L. a-, short for ab "away from" (e.g. avert), or its cognate, Gk. a-, short for apo "away from, from," both cognate with Skt. apa "away from," Goth. af, O.E. of (see APO- (Cf. apo-)).

{{12}}a- (3) prefix meaning "not," from Gk. a-, an- "not," from PIE root *ne "not" (see UN- (Cf. un-)).