1. [n]  a nervous restrained laugh
2. [v]  laugh nervously

TITTER is a 6 letter word that starts with T.

1. \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.
   
   

2. \Tit"ter\, n.
   A restrained laugh. ``There was a titter of . . . delight on
   his countenance.'' --Coleridge.
   
   

3. \Tit"ter\, v. i.
   To seesaw. See {Teeter}.