Yes, TALLIS is a Scrabble word!

Letter values in Scrabble US: T 1, A 1, L 1, L 1, I 1, S 1.

Is it a valid word?

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

English organist and composer of church and secular music; was granted a monopoly in music printing with William Byrd (1505-1585)
(Judaism) a shawl with a ritually knotted fringe at each corner; worn by Jews at morning prayer

Also: thomas tallis, prayer shawl.