Yes, DUALITY is a Scrabble word!

Letter values in Scrabble US: D 2, U 1, A 1, L 1, I 1, T 1, Y 4.

Is it a valid word?

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

being twofold; a classification into two opposed parts or subclasses
(physics) the property of matter and electromagnetic radiation that is characterized by the fact that some properties can be explained best by wave theory and others by particle theory
(geometry) the interchangeability of the roles of points and planes in the theorems of projective geometry

Also: wave-particle duality.