Source : Webster's Revised Unabridged Dictionary (1913)

Diffident \Dif"fi*dent\, a. [L. diffidens, -entis, p. pr. of
   diffidere; dif- = dis + fidere to trust; akin to fides faith.
   See {Faith}, and cf. {Defy}.]
   1. Wanting confidence in others; distrustful. [Archaic]

            You were always extremely diffident of their
            success.                              --Melmoth.

   2. Wanting confidence in one's self; distrustful of one's own
      powers; not self-reliant; timid; modest; bashful;
      characterized by modest reserve.

            The diffident maidens, Folding their hands in
            prayer.                               --Longfellow.

   Syn: Distrustful; suspicious; hesitating; doubtful; modest;
        bashful; lowly; reserved.

Source : WordNet®

diffident
     adj 1: showing modest reserve; "she was diffident when offering a
            comment on the professor's lecture"
     2: lacking self-confidence; "stood in the doorway diffident and
        abashed"; "problems that call for bold not timid
        responses"; "a very unsure young man" [syn: {shy}, {timid},
         {unsure}]