Yes, CLASSICISMS is a Scrabble word!

Letter values in Scrabble US: C 3, L 1, A 1, S 1, S 1, I 1, C 3, I 1, S 1, M 3, S 1.

Is it a valid word?

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

a movement in literature and art during the 17th and 18th centuries in Europe that favored rationality and restraint and strict forms

Not playable in Scrabble US: CLASSICALISM.