Yes, DECADE is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, C 3, A 1, D 2, E 1.

Is it a valid word?

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

a period of 10 years
the cardinal number that is the sum of nine and one; the base of the decimal system

Also: 10, x.