OXFORD DICTIONARY
a-, prefix not, without (amoral; agnostic; apetalous).
a-, prefix implying motion onward or away, adding intensity to verbs of motion (arise; awake).
a-, prefix to, at, or into a state (adroit; agree; amass; avenge).
a-, prefix.
1 from, away (abridge).
2 of (akin; anew).
3 out, utterly (abash; affray).
4 in, on, engaged in, etc. (see A(2)).
a-, prefix assim. form of AD- before sc, sp, st.