tit·ter /ˈtɪtɚ/
  嗤笑,偷笑(vi.)吃吃地笑,偷笑
  Tit·ter v. t. [imp. & p. p. Tittered p. pr. & vb. n. Tittering.]  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.
  Tit·ter, n. A restrained laugh. “There was a titter of . . . delight on his countenance.”
  Tit·ter, v. i. To seesaw. See Teeter.
  ◄ ►
  titter
       n : a nervous restrained laugh
       v : laugh nervously; "The girls giggled when the rock star came
           into the classroom" [syn: giggle]