Yes, ADHESION is a Scrabble word!

Letter values in Scrabble US: A 1, D 2, H 4, E 1, S 1, I 1, O 1, N 1.

Is it a valid word?

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

abnormal union of bodily tissues; most common in the abdomen
a fibrous band of scar tissue that binds together normally separate anatomical structures
the property of sticking together (as of glue and wood) or the joining of surfaces of different composition
faithful support for a cause or political party or religion