sly

Definitions:

Artfully cunning; crafty; artfully dexterous in performing things secretly and escaping observation; done with artful and dexterous secrecy; marked with artful secrecy.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)
Slyly, slily.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)
SLYLY or SLILY.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adverb) (adv.) (adverb)
Slyer.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (comp.) (comparative)
Artful; cunning; secret.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)
Slily.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)
Secretly mischievous; underhand and crafty; deceitful; playfully mischievous; roguish.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Slyness.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
Dexterous in doing anything so as to be unobserved: cunning: wily: secret: done with artful dexterity.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Cunning; artful; crafty; clever in doing things secretly and escaping detection, usually implying meanness.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Slyest.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (superl.) (superlative)

Usage examples:

But Old John got to look sly and wink at my father when we came to this question, out of the hundred others.
- Wandering Heath by Sir Arthur Thomas Quiller-Couch
" The great point is, after all, to learn the young lady's disposition in the matter-" " Ah, Charley, none of this with me, you sly dog!
- Charles O'Malley, The Irish Dragoon, Volume 2 (of 2) by Charles Lever
The owl spread out his silent, soft, sly wings, and lighting between Tricksey- Wee and Buffy- Bob, nearly smothered them, closing up one under each wing.
- The Light Princess and Other Fairy Stories by George MacDonald