whim

Short definition from Wiktionary

Noun

1. 1
   A fanciful impulse, or sudden change of idea.
2. 2
   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
3. 3
   A bird, the Eurasian wigeon.
4. 4
   Initialism of warm-hot intergalactic medium.

Verb

1. 1
   To be seized with a whim; to be capricious.