Yes, TONTINE is a Scrabble word!

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

Is it a valid word?

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

a form of life insurance whereby on the death or default of a participant his share is distributed to the remaining members
an annuity scheme wherein participants share certain benefits and on the death of any participant his benefits are redistributed among the remaining participants; can run for a fixed period of time or until the death of all but one participant

Also: tontine insurance.