Yes, PALIMPSESTS is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, L 1, I 1, M 3, P 3, S 1, E 1, S 1, T 1, S 1.

Is it a valid word?

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

a manuscript (usually written on papyrus or parchment) on which more than one text has been written with the earlier writing incompletely erased and still visible