Yes, MONITION is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, N 1, I 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

a firm rebuke
cautionary advice about something imminent (especially imminent danger or other unpleasantness)
a summons issued after the filing of a libel or claim directing all parties concerned to show cause why the judgment asked for should not be granted

Also: word of advice, process of monition.