The Collaborative International Dictionary of English v.0.48:

Laughter \Laugh"ter\, n. [AS. hleahtor; akin to OHG. hlahtar, G.
   gel[aum]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.
   [1913 Webster]

         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.
   [1913 Webster]

         Archly the maiden smiled, and with eyes overrunning
         with laughter.                           --Longfellow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "laughter":
   Homeric laughter, amusement, belly laugh, boff, boffola,
   burst of laughter, cachinnation, cackle, chortle, chortling,
   chuckle, convulsion, crow, fit of laughter, frivolity, fun,
   gales of laughter, giggle, glee, gleefulness, guffaw, ha-ha,
   hearty laugh, hee-haw, hee-hee, high glee, hilariousness, hilarity,
   ho-ho, horselaugh, jocularity, jocundity, jolliness, jollity,
   joviality, joy, joyfulness, joyousness, laugh, laughing, levity,
   merriment, merriness, mirth, mirthfulness, outburst of laughter,
   peal of laughter, risibility, roar of laughter, shout,
   shout of laughter, shriek, snicker, snickering, snigger,
   sniggering, snort, tee-hee, titter, yuck, yuk-yuk



The Devil's Dictionary (1881-1906):

LAUGHTER, n.  An interior convulsion, producing a distortion of the
features and accompanied by inarticulate noises.  It is infectious
and, though intermittent, incurable.  Liability to attacks of laughter
is one of the characteristics distinguishing man from the animals --
these being not only inaccessible to the provocation of his example,
but impregnable to the microbes having original jurisdiction in
bestowal of the disease.  Whether laughter could be imparted to
animals by inoculation from the human patient is a question that has
not been answered by experimentation.  Dr. Meir Witchell holds that
the infection character of laughter is due to the instantaneous
fermentation of _sputa_ diffused in a spray.  From this peculiarity he
names the disorder _Convulsio spargens_.