Yes, slyly is a Scrabble word!
...and is worth 11 points in Scrabble, and 11 points in Words with Friends
slyly
Adverb
1. In an artful manner
What Scrabble words can I make with the letters in slyly?
3 Letter Words
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Words that can be created with an extra letter added to slyly:
X:xylyls