Yes, MUSTHS is a Scrabble word!

Letter values in Scrabble US: M 3, U 1, S 1, T 1, H 4, S 1.

Is it a valid word?

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

an annual phase of heightened sexual excitement in the males of certain large mammals (especially elephants); is associated with discharge from a gland between the eye and ear