What does Sly mean?
Sly /sly/ [1 syll.] as a name for boys is of Latin derivation, and the name Sly means "of the woods". Sly is a variant form of Sylvester (Latin). Compare last name Slay.
How popular is Sly?
Sly is an uncommonly occurring first name for men but a very prominent last name for both adults and children (#9325 out of 150436, Top 6%). (2000 U.S. Census)
The only popular variation form of Sly (unlisted) ranked in the Top 1000 is Sylvester. Adoption of this boy name reached its highest during 1890-1899 (usage of 0.847%) and is now significantly less, with Sylvester becoming less in vogue. Below is a graphed comparison of the usage of the boy name Sly and related names. (2014 Birth Statistics)