Yes, diss is a Scrabble word!
...and is worth 5 points in Scrabble, and 5 points in Words with Friends
diss
Verb
1. Treat, mention, or speak to rudely
Noun
1. God of the underworld; counterpart of Greek Pluto
What Scrabble words can I make with the letters in diss?
3 Letter Words
2 Letter Words