Yes, RELATION is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, L 1, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

an abstraction belonging to or characteristic of two entities or parts together
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
a person related by blood or marriage
an act of narration
(law) the principle that an act done at a later time is deemed by law to have occurred at an earlier time
(usually plural) mutual dealings or connections among persons or groups

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