Yes, SYNERGISM is a Scrabble word!

Letter values in Scrabble US: S 1, Y 4, N 1, E 1, R 1, G 2, I 1, S 1, M 3.

Is it a valid word?

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

the working together of two things (muscles or drugs for example) to produce an effect greater than the sum of their individual effects
the theological doctrine that salvation results from the interaction of human will and divine grace