Source : Webster's Revised Unabridged Dictionary (1913)

Wiseacre \Wise"a*cre\, n. [OD. wijssegger or G. weissager a
   foreteller, prophet, from weissagen to foretell, to prophesy,
   OHG. w[=i]ssag?n, corrupted (as if compounded of the words
   for wise and say) fr. w[=i]zzag?n, fr. w[=i]zzag? a prophet,
   akin to AS. w[=i]tiga, w[=i]tga, from the root of E. wit. See
   {Wit}, v.]
   1. A learned or wise man. [Obs.]

            Pythagoras learned much . . . becoming a mighty
            wiseacre.                             --Leland.

   2. One who makes undue pretensions to wisdom; a would-be-wise
      person; hence, in contempt, a simpleton; a dunce.

Source : WordNet®

wiseacre
     n : an upstart who makes conceited, sardonic, insolent comments
         [syn: {wise guy}, {smart aleck}, {wisenheimer}, {weisenheimer}]