sly

Short definition from Wiktionary

Adjective

1. 1
   Artfully cunning; secretly mischievous; wily.
2. 2
   Dexterous in performing an action, so as to escape notice
3. 3
   Done with, and marked by, artful and dexterous secrecy; subtle
4. 4
   Light or delicate; slight; thin.

Adverb

1. 1
   Slyly.

Proper noun

1. 1
   A diminutive of the male given name Sylvester.
2. 2
   A surname