Yes, MODALITY is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, D 2, A 1, L 1, I 1, T 1, Y 4.

Is it a valid word?

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

a classification of propositions on the basis of whether they claim necessity or possibility or impossibility
verb inflections that express how the action or state is conceived by the speaker
a particular sense
a method of therapy that involves physical or electrical therapeutic treatment

Also: sense modality, sensory system.