Source : Webster's Revised Unabridged Dictionary (1913)

Laughter \Laugh"ter\, n. [AS. hleahtor; akin to OHG. hlahtar, G.
   gel["a]chter, Icel. hl[=a]tr, Dan. latter. See {Laugh}, v. i.
   ]
   A movement (usually involuntary) of the muscles of the face,
   particularly of the lips, with a peculiar expression of the
   eyes, indicating merriment, satisfaction, or derision, and
   usually attended by a sonorous and interrupted expulsion of
   air from the lungs. See {Laugh}, v. i.

         The act of laughter, which is a sweet contraction of
         the muscles of the face, and a pleasant agitation of
         the vocal organs, is not merely, or totally within the
         jurisdiction of ourselves.               --Sir T.
                                                  Browne.

         Archly the maiden smiled, and with eyes overrunning
         with laughter.                           --Longfellow.

Source : WordNet®

laughter
     n 1: the sound of laughing [syn: {laugh}]
     2: the activity of laughing; the manifestation of joy or mirth
        of scorn; "he enjoyed the laughter of the crowd"