whim in WordNet English dictionary

1. a sudden desire
   "he bought it on an impulse"
   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"
   notion  whim  whimsy  whimsey