Yes, WASHBOARD is a Scrabble word!

Letter values in Scrabble US: W 4, A 1, S 1, H 4, B 3, O 1, A 1, R 1, D 2.

Is it a valid word?

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

device consisting of a corrugated surface to scrub clothes on
protective covering consisting of a broad plank along a gunwale to keep water from splashing over the side