Yes, only is a Scrabble word!
...and is worth 7 points in Scrabble, and 8 points in Words with Friends
only
Adverb
1. And nothing more
2. Without any others being included or involved
3. With nevertheless the final result
4. In the final outcome
5. Except that; only this time she came out better"
6. Never except when
7. As recently as
Adjective
1. Being the only one; single and isolated from others
2. Exclusive of anyone or anything else
What Scrabble words can I make with the letters in only?
3 Letter Words
2 Letter Words