The Collaborative International Dictionary of English v.0.48:

Chortle \Chor"tle\, v. t. & i. [imp. & p. p. Chortled; p. pr.
   & vb. n. Chor"tling.]
   A word coined by Lewis Carroll (Charles L. Dodgson), and
   usually explained as a combination of chuckle and snort.
   [Humorous]

         O frabjous day ! Callooh ! Callay !
         He chortled in his joy.                  --Lewis
                                                  Carroll.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

chortle
    n 1: a soft partly suppressed laugh [syn: chortle, chuckle]
    v 1: laugh quietly or with restraint [syn: chuckle, chortle,
         laugh softly]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "chortle":
   Homeric laughter, be in stitches, belly laugh, boff, boffola,
   break up, burst into laughter, burst of laughter, burst out,
   burst out laughing, burst with laughter, bust a gut, cachinnate,
   cachinnation, cackle, chuckle, convulsion, crow, fit of laughter,
   gales of laughter, giggle, go into convulsions, guffaw, ha-ha,
   hearty laugh, hee-haw, hee-hee, hilarity, ho-ho, horselaugh, laugh,
   laugh it up, laugh outright, laughing, laughter,
   nearly die laughing, outburst of laughter, peal of laughter,
   risibility, roar, roar of laughter, roar with laughter,
   shake like jelly, shake with laughter, shout, shout of laughter,
   shriek, snicker, snigger, sniggle, snort, split,
   split with laughter, tee-hee, titter, yuck, yuk-yuk