Yes, WHIMSEY is a Scrabble word!

Letter values in Scrabble US: W 4, H 4, I 1, M 3, S 1, E 1, Y 4.

Is it a valid word?

WHIMSEY is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an odd or fanciful or capricious idea
the trait of acting unpredictably and more from whim or caprice than from reason or judgment