Yes, PURITANISM is a Scrabble word!

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

Is it a valid word?

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

the beliefs and practices characteristic of Puritans (most of whom were Calvinists who wished to purify the Church of England of its Catholic aspects)
strictness and austerity in conduct and religion