Yes, ECUMENICISM is a Scrabble word!

Letter values in Scrabble US: E 1, C 3, U 1, M 3, E 1, N 1, I 1, C 3, I 1, S 1, M 3.

Is it a valid word?

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

(Christianity) the doctrine of the ecumenical movement that promotes cooperation and better understanding among different religious denominations: aimed at universal Christian unity