Yes, SYNCRETISMS is a Scrabble word!

Letter values in Scrabble US: S 1, Y 4, N 1, C 3, R 1, E 1, T 1, I 1, S 1, M 3, S 1.

Is it a valid word?

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

the union (or attempted fusion) of different systems of thought or belief (especially in religion or philosophy)
the fusion of originally different inflected forms (resulting in a reduction in the use of inflections)