Yes, TERRORIST is a Scrabble word!

Letter values in Scrabble US: T 1, E 1, R 1, R 1, O 1, R 1, I 1, S 1, T 1.

Is it a valid word?

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

a radical who employs terror as a political weapon; usually organizes with other terrorists in small cells; often uses religion as a cover for terrorist activities