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]

The Collaborative International Dictionary of English v.0.48:

Titter \Tit"ter\, n.
   A restrained laugh. "There was a titter of . . . delight on
   his countenance." --Coleridge.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Titter \Tit"ter\, v. i.
   To seesaw. See Teeter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

titter
    n 1: a nervous restrained laugh
    v 1: laugh nervously; "The girls giggled when the rock star came
         into the classroom" [syn: giggle, titter]