Yes, PROBABILITY is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, O 1, B 3, A 1, B 3, I 1, L 1, I 1, T 1, Y 4.

Is it a valid word?

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

a measure of how likely it is that some event will occur; a number expressing the ratio of favorable cases to the whole number of cases possible
the quality of being probable; a probable event or the most probable event