The Collaborative International Dictionary of English v.0.48:

Ab- \Ab-\ ([a^]b). [Latin prep., etymologically the same as E.
   of, off. See Of.]
   A prefix in many words of Latin origin. It signifies from,
   away, separating, or departure, as in abduct, abstract,
   abscond. See A-(6).
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ab \Ab\ ([a^]b), n. [Of Syriac origin.]
   The fifth month of the Jewish year according to the
   ecclesiastical reckoning, the eleventh by the civil
   computation, coinciding nearly with August. --W. Smith.
   [1913 Webster]