Yes, PLURALISMS is a Scrabble word!

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

Is it a valid word?

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

a social organization in which diversity of racial or religious or ethnic or cultural groups is tolerated
the doctrine that reality consists of several basic substances or elements
the practice of one person holding more than one benefice at a time