Yes, CONJUNCTION is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, J 8, U 1, N 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

the temporal property of two things happening at the same time
the state of being joined together
an uninflected function word that serves to conjoin words or phrases or clauses or sentences
the grammatical relation between linguistic units (words or phrases or clauses) that are connected by a conjunction
(astronomy) apparent meeting or passing of two or more celestial bodies in the same degree of the zodiac
something that joins or connects

Also: co-occurrence.