Yes, TREMENDOUS is a Scrabble word!

Letter values in Scrabble US: T 1, R 1, E 1, M 3, E 1, N 1, D 2, O 1, U 1, S 1.

Is it a valid word?

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

extraordinarily large in size or extent or amount or power or degree; that a whole civilization should be dependent on technology"- Walter Lippman
extraordinarily good or great; used especially as intensifiers
extreme in degree or extent or amount or impact