Yes, ECUMENISM is a Scrabble word!

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

Is it a valid word?

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

a movement promoting union between religions (especially between Christian churches)
(Christianity) the doctrine of the ecumenical movement that promotes cooperation and better understanding among different religious denominations: aimed at universal Christian unity

Not playable in Scrabble US: OECUMENISM.