caprice

Short definition from Wiktionary

Noun

1. 1
   An impulsive, seemingly unmotivated action, change of mind, or notion.
2. 2
   A brief romance.
3. 3
   An unpredictable or sudden condition, change, or series of changes.
4. 4
   A disposition to be impulsive.
5. 5
   A capriccio.

Proper noun

1. 1
   A female given name.