Yes, REMISSION is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, M 3, I 1, S 1, S 1, I 1, O 1, N 1.

Is it a valid word?

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

an abatement in intensity or degree (as in the manifestations of a disease)
a payment of money sent to a person in another place
(law) the act of remitting (especially the referral of a law case to another court)
the act of absolving or remitting; formal redemption as pronounced by a priest in the sacrament of penance

Also: remission of sin.