Yes, SIDEBOARD is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, D 2, E 1, B 3, O 1, A 1, R 1, D 2.

Is it a valid word?

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

a removable board fitted on the side of a wagon to increase its capacity
a board that forms part of the side of a bed or crib
a piece of furniture that stands at the side of a dining room; has shelves and drawers