Latin (and French) Prefixes.
A-, ab-, (ab-s-), away from: avert, absent, ab-s-tract; Fr., avaunt.
Ad-, (Fr. a-) (-d is often changed because of the influence of the following consonant), to: adapt, abbreviate, accord, affect, aggression, allude, annul, arrogate, attain; Fr., achieve, acquaint, amount.
Amb- or am-, around, round about, (both): ambition (lit. going about, canvassing), ambiguous, ambidextrous, amputate (to cut around).
Ante-, before: antedate, ante-room, anticipate; Fr., an- in ancestor = antecessor.
Bis- and bi-, twice, two: bias (= two-faced), biped, bisect, biscuit (= twice baked).
Circum-, around: circumference, circuit, circulate, circumvent.
Cum-, with, takes the forms com-, con-, col-, co-, cor-, under the influence of the letter following: compound, concord, collect, coöperate, correct, counsel.
Contra-, against: contradict; Fr., controvert, counterfeit.
De-, down, from: decline, deduct, decamp. It is negative in derange, deform, destroy; intensive in declare, deprave, despoil, desolate, desiccate.