Yes, AORISTS is a Scrabble word!

Letter values in Scrabble US: A 1, O 1, R 1, I 1, S 1, T 1, S 1.

Is it a valid word?

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

a verb tense in some languages (classical Greek and Sanskrit) expressing action (especially past action) without indicating its completion or continuation