Yes, CONTRACTION is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, T 1, R 1, A 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

(physiology) a shortening or tensing of a part or organ (especially of a muscle or muscle fiber)
the process or result of becoming smaller or pressed together
a word formed from two or more words by omitting or combining some sounds
the act of decreasing (something) in size or volume or quantity or scope

Also: muscular contraction, muscle contraction.