Sly is an adjective, meaning one of the following:

1. Clever in practical matters.
2. Hiding ones true intentions or goals.

Its synonyms are "cunning" and "roughish".

Search the Wikitionary for more information about the word "sly".

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Sly is also a proper masculine name, short for Sylvester. It is the name of several famous persons:

• Sly Stone, American musician, frontman for Sly & the Family Stone
• Sylvester "Sly" Stallone, American actor.