Source : Webster's Revised Unabridged Dictionary (1913)

Titter \Tit"ter\, v. t. [imp. & p. p. {Tittered}; p. pr. & vb.
   n. {Tittering}.] [Probably of imitative origin.]
   To laugh with the tongue striking against the root of the
   upper teeth; to laugh with restraint, or without much noise;
   to giggle.

         A group of tittering pages ran before.   --Longfellow.

Source : WordNet®

tittering
     adj : being or sounding of nervous or suppressed laughter [syn: {thoriated}]