Yes, BYZANTINE is a Scrabble word!

Letter values in Scrabble US: B 3, Y 4, Z 10, A 1, N 1, T 1, I 1, N 1, E 1.

Is it a valid word?

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

of or relating to the Eastern Orthodox Church or the rites performed in it
of or relating to or characteristic of the Byzantine Empire or the ancient city of Byzantium
highly complex or intricate and occasionally devious