The Collaborative International Dictionary of English v.0.48:

Knickknack \Knick"knack`\, n. [See Knack.]
   A trifle or toy; a bawble; a gewgaw; a tchotchke.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

knickknack
    n 1: a small inexpensive mass-produced article [syn:
         knickknack, novelty]
    2: miscellaneous curios [syn: bric-a-brac, knickknack,
       nicknack, knickknackery, whatnot]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "knickknack":
   a continental, a curse, a damn, a darn, a hoot, agate, bagatelle,
   ball, baseball bat, bat, battledore, bauble, bean, bibelot, bit,
   blocks, brass farthing, bric-a-brac, button, cent, checkerboard,
   chessboard, club, cockhorse, cosmetics, cricket bat, cue, curio,
   dido, doll, doll carriage, farce, farthing, feather, fig, fleabite,
   folderol, fribble, frippery, gaud, gewgaw, giftware, gimcrack,
   golf club, hair, halfpenny, hill of beans, hobbyhorse,
   jack-in-the-box, jacks, jackstones, jackstraws, jest, joke,
   kickshaw, knack, knickknackery, knickknacks, marble, marionette,
   mig, miniature, minikin, mockery, molehill, notion, notions,
   novelties, novelty, odds and ends, paper doll, peppercorn,
   picayune, pick-up sticks, pin, pinch of snuff, pinprick, pinwheel,
   plaything, pretty-pretty, puppet, racket, rag doll, rap, red cent,
   rocking horse, row of pins, rush, shit, snap, sneeshing, sou,
   souvenir, sport, steelie, straw, sundries, taw, teetotum,
   toilet goods, toiletries, top, toy, toy soldier, trifle, trinket,
   triviality, trumpery, tuppence, two cents, twopence, virtu,
   whatnot, whim-wham