Толковый словарь английского языка Oxford English Reference - a-

1. prefix not, without (amoral; agnostic; apetalous). Etymology: Gk a-, or L f. Gk, or F f. L f. Gk 2. prefix implying motion onward or away, adding intensity to verbs of motion (arise; awake). Etymology: OE a-, orig. ar- 3. prefix to, at, or into a state (adroit; agree; amass; avenge). Etymology: ME a- (= OF prefix a-), (f. F) f. L ad- to, at 4. prefix. 1 from, away (abridge). 2 of (akin; anew). 3 out, utterly (abash; affray). 4 in, on, engaged in, etc. (see A(2)). Etymology: sense 1 f. ME a-, OF a-, f. L ab; sense 2 f. ME a- f. OE of prep.; sense 3 f. ME, AF a- = OF e-, es- f. L ex 5. prefix assim. form of AD- before sc, sp, st.