whimsy

Short definition from Wiktionary

Noun

1. 1
   A quaint and fanciful idea; a whim; playfully odd behaviour.
2. 2
   An impulsive, illogical or capricious character.
3. 3
   A whim (capstan or vertical drum).
4. 4
   A jigsaw puzzle piece that has been cut into a recognizable shape, as if on a whim; often the shape is representative of the theme of the image used for the puzzle.
5. 5
   The support that protects a finished piece as it is detached from a punty.

Verb

1. 1
   To fill with whimsies or whims; to make fantastic; to craze.

Adjective

1. 1
   Synonym of whimsical.