a- /e-, æ-, ə-/ 前綴
 非, 不, 無, 缺, 離 (在子音前)
 a- /ə-/ 前綴
 處於…狀態, 在…之上, 到…;
 表示加強語氣及 at, in, on, to 等含義
 A
 A暫存器(同register,arithmetic)
 A-. 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-.
 Note: Besides these, there are other sources from which the prefix a takes its origin.
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 A
      n 1: the blood group whose red cells carry the A antigen [syn: type
           A, group A]
      2: a metric unit of length equal to one ten billionth of a
         meter (or 0.0001 micron); used to specify wavelengths of
         electromagnetic radiation [syn: angstrom, angstrom unit]
      3: any of several fat-soluble vitamins essential for normal
         vision; prevents night blindness or inflammation or
         dryness of the eyes [syn: vitamin A, antiophthalmic
         factor, axerophthol]
      4: one of the four nucleotides used in building DNA; all four
         nucleotides have a common phosphate group and a sugar
         (ribose) [syn: deoxyadenosine monophosphate]
      5: (biochemistry) purine base found in DNA and RNA; pairs with
         thymine in DNA and with uracil in RNA [syn: adenine]
      6: the basic unit of electric current adopted under the Systeme
         International d'Unites; "a typical household circuit
         carries 15 to 50 amps" [syn: ampere, amp]
      7: the 1st letter of the Roman alphabet
 A
    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.