Yes, THYMUSES is a Scrabble word!

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

Is it a valid word?

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

large genus of Old World mints: thyme
a ductless glandular organ at the base of the neck that produces lymphocytes and aids in producing immunity; atrophies with age

Also: genus thymus, thymus gland.