Yes, TREFOIL is a Scrabble word!

Letter values in Scrabble US: T 1, R 1, E 1, F 4, O 1, I 1, L 1.

Is it a valid word?

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

any of several Old World herbs of the genus Medicago having small flowers and trifoliate compound leaves
a plant of the genus Trifolium
an architectural ornament in the form of three arcs arranged in a circle