Yes, CAESARISMS is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, E 1, S 1, A 1, R 1, I 1, S 1, M 3, S 1.

Is it a valid word?

CAESARISMS is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

a form of government in which the ruler is an absolute dictator (not restricted by a constitution or laws or opposition etc.)

Also: authoritarianism, one-man rule.

Not playable in Scrabble US: STALINISM.