Yes, COITUS is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, I 1, T 1, U 1, S 1.

Is it a valid word?

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

the act of sexual procreation between a man and a woman; the man's penis is inserted into the woman's vagina and excited until orgasm and ejaculation occur

Also: sexual intercourse, sex act, sexual congress, sexual relation, carnal knowledge.