Yes, FONDUS is a Scrabble word!

Letter values in Scrabble US: F 4, O 1, N 1, D 2, U 1, S 1.

Is it a valid word?

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

cubes of meat or seafood cooked in hot oil and then dipped in any of various sauces
hot cheese or chocolate melted to the consistency of a sauce into which bread or fruits are dipped