Yes, TERRORISM 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, M 3.

Is it a valid word?

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

the calculated use of violence (or the threat of violence) against civilians in order to attain goals that are political or religious or ideological in nature; this is done through intimidation or coercion or instilling fear

Also: act of terrorism, terrorist act.