The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         A group of tittering pages ran before.   --Longfellow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tittering
    adj 1: being or sounding of nervous or suppressed laughter [syn:
           thoriated, tittering]