The Collaborative International Dictionary of English v.0.48:

brainstorm \brain"storm`\ n.
   the clear (and often sudden) understanding of a complex
   situation; a sudden brilliant insight.

   Syn: insight, brainwave.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

brainstorm \brain"storm`\ v. t. & i.
   to try to solve a problem by discussing it exhaustively in an
   intense group meeting encouraging uninhibited and spontaneous
   contributions from all members.

   Syn: practice brainstorming.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

brainstorm
    n 1: the clear (and often sudden) understanding of a complex
         situation [syn: insight, brainstorm, brainwave]
    v 1: try to solve a problem by thinking intensely about it

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "brainstorm":
   absurd idea, afebrile delirium, automatic response, blind impulse,
   boutade, brain wave, brainchild, bright idea, bright thought,
   brilliant idea, capriccio, caprice, conceit, crank, craze,
   crazy idea, crotchet, deliriousness, delirium, drive, fad, fancy,
   fantastic notion, fantasy, flash, fleeting impulse, flimflam,
   fool notion, freak, freakish inspiration, good idea, gut response,
   harebrained idea, humor, impulse, incoherence, inspiration,
   instinct, involuntary impulse, kink, lingual delirium, maggot,
   megrim, natural impulse, notion, passing fancy, quick hunch, quirk,
   ranting, raving, reflex, sudden thought, toy, urge, vagary,
   wandering, whim, whim-wham, whimsy