Yes, THREATEN is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, R 1, E 1, A 1, T 1, E 1, N 1.

Is it a valid word?

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

pose a threat to; present a danger to
to utter intentions of injury or punishment against:"He threatened me when I tried to call the police"
to be a menacing indication of something:"The clouds threaten rain"