Yes, PROBABILISM is a Scrabble word!

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

Is it a valid word?

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

a Roman Catholic system of casuistry that when expert opinions differ an actor can follow any solidly probable opinion that he wishes even though some different opinion might be more probable
(philosophy) the doctrine that (since certainty is unattainable) probability is a sufficient basis for belief and action