Yes, TANGENT is a Scrabble word!

Letter values in Scrabble US: T 1, A 1, N 1, G 2, E 1, N 1, T 1.

Is it a valid word?

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

a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point
ratio of the opposite to the adjacent side of a right-angled triangle