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. ofd/ne off the dun or hill). (3) AS.
   a- (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 a (L. ad
   to), as in abase, achieve. (6) L. a, ab, abs, from, as in avert. (7)
   Greek insep. prefix / without, or privative, not, as in abyss, atheist;
   akin to E. un-.