Yes, BINOMIAL is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, N 1, O 1, M 3, I 1, A 1, L 1.

Is it a valid word?

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

(mathematics) a quantity expressed as a sum or difference of two terms; a polynomial with two terms

of or relating to or consisting of two terms
having or characterized by two names, especially those of genus and species in taxonomies

Not playable in Scrabble US: BINOMINAL.