The Collaborative International Dictionary of English v.0.48:

Whim \Whim\, n. [Cf. Whimbrel.] (Zool.)
   The European widgeon. [Prov. Eng.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whim \Whim\, n. [Cf. Icel. hwima to wander with the eyes, vim
   giddiness, Norw. kvima to whisk or flutter about, to trifle,
   Dan. vimse to skip, whisk, jump from one thing to another,
   dial. Sw. hvimsa to be unsteady, dizzy, W. chwimio to move
   briskly.]
   [1913 Webster]
   1. A sudden turn or start of the mind; a temporary
      eccentricity; a freak; a fancy; a capricious notion; a
      humor; a caprice.
      [1913 Webster]

            Let every man enjoy his whim.         --Churchill.
      [1913 Webster]

   2. (Mining) A large capstan or vertical drum turned by horse
      power or steam power, for raising ore or water, etc., from
      mines, or for other purposes; -- called also whim gin,
      and whimsey.
      [1913 Webster]

   Whim gin (Mining), a whim. See Whim, 2.

   Whim shaft (Mining), a shaft through which ore, water,
      etc., is raised from a mine by means of a whim.
      [1913 Webster]

   Syn: Freak; caprice; whimsey; fancy.

   Usage: Whim, Freak, Caprice. Freak denotes an
          impulsive, inconsiderate change of mind, as by a child
          or a lunatic. Whim is a mental eccentricity due to
          peculiar processes or habits of thought. Caprice is
          closely allied in meaning to freak, but implies more
          definitely a quality of willfulness or wantonness.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whim \Whim\, v. i.
   To be subject to, or indulge in, whims; to be whimsical,
   giddy, or freakish. [R.] --Congreve.
   [1913 Webster]

WordNet (r) 3.0 (2006):

whim
    n 1: a sudden desire; "he bought it on an impulse" [syn:
         caprice, impulse, whim]
    2: an odd or fanciful or capricious idea; "the theatrical notion
       of disguise is associated with disaster in his stories"; "he
       had a whimsy about flying to the moon"; "whimsy can be
       humorous to someone with time to enjoy it" [syn: notion,
       whim, whimsy, whimsey]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "whim":
   apparition, bee, boutade, brainchild, brainstorm, bubble,
   capriccio, caprice, chimera, conceit, crank, craze, crazy idea,
   crotchet, delirium, disposition, dream, eidolon, fad, fancy,
   fantasque, fantastic notion, fantasy, fiction, figment, flimflam,
   fool notion, freak, freakish inspiration, hallucination,
   harebrained idea, humor, idea, idle fancy, illusion, imagery,
   imagination, imagining, inclination, insubstantial image,
   invention, kink, maggot, make-believe, megrim, myth, notion,
   passing fancy, phantasm, phantom, quirk, romance, sick fancy,
   thick-coming fancies, thought, toy, trip, vagary, vapor, vision,
   whim-wham, whimsy, wildest dreams