Yes, tass is a Scrabble word!
...and is worth 4 points in Scrabble, and 4 points in Words with Friends
tass
Noun
1. A hard grey lustrous metallic element that is highly resistant to corrosion; occurs in niobite and fergusonite and tantalite
What Scrabble words can I make with the letters in tass?
3 Letter Words
2 Letter Words