Yes, hiss is a Scrabble word!
...and is worth 7 points in Scrabble, and 6 points in Words with Friends
hiss
Verb
1. Make a sharp hissing sound, as if to show disapproval
2. Move with a whooshing sound
3. Express or utter with a hiss
4. Show displeasure, as after a performance or speech
Noun
1. A fricative sound (especially as an expression of disapproval)
2. A cry or noise made to express displeasure or contempt
What Scrabble words can I make with the letters in hiss?
3 Letter Words
2 Letter Words