What does Sly mean?
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 these boy names 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)