whim·sy also whim·sey 
(wĭmzē, hwĭm-)
(wĭmzē, hwĭm-)n. pl. whim·sies also whim·seys
1. An unusual, unexpected, or fanciful idea; a whim.
2. Quaint, fanciful, or playful humor: stories full of whimsy.
[Probably from whim-wham, fanciful object.]