sly

adj. crafty, cunning; secretive, stealthy; mischievous, playful

Sly is an adjective, meaning one of the following:Clever in practical matters.Hiding ones true intentions or goals.Its synonyms are "cunning" and "roguish".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.Sylvain Grenier, Canadian professional wrestler.William Sly, Elizabethan actor and colleague of William Shakespeare.Sly (goblin character), a fictional character created by Enid Blyton.
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Adjective
1. marked by skill in deception; "cunning men often pass for wise"; "deep political machinations"; "a foxy scheme"; "a slick evasive answer"; "sly as a fox"; "tricky Dik"; "a wily old attorney"
(synonym) crafty, cunning, dodgy, foxy, guileful, knavish, slick, tricksy, tricky, wily
(similar) artful

(v. t.)
Light or delicate; slight; thin.
  

(v. t.)
Done with, and marked by, artful and dexterous secrecy; subtle; as, a sly trick.
  

(v. t.)
Dexterous in performing an action, so as to escape notice; nimble; skillful; cautious; shrewd; knowing; -- in a good sense.
  

(v. t.)
Artfully cunning; secretly mischievous; wily.
  

(adv.)
Slyly.
  

Synonyms and related words:
Byzantine, Machiavellian, Machiavellic, acute, adroit, arch, artful, astute, back-door, backstairs, cagey, calculating, canny, clandestine, clever, covert, crafty, creep, crooked, cunning, cute, deceitful, deep, deep-laid, designing, devious, dexterous, diplomatic, dishonest, disingenuous, downy, feline, foxy, furtive, guileful, gumshoe, hidlings, hole-and-corner, hugger-mugger, ingenious, insidious, inventive, knowing, lurk, masterful, pawky, politic, predatory, privy, quiet, ready, resourceful, scheming, serpentine, shady, sharp, shifty, shrewd, skulk, skulking, slick, slide, slim, slink, slinking, slinky, slippery, smart, smooth, snake, snaky, sneaking, sneaky, snook, sophistical, steal, stealthy, strategic, subtile, subtle, supple, surreptitious, tactical, trickish, tricksy, tricky, under-the-counter, under-the-table, undercover, underground, underhand, underhanded, unfrank, unobtrusive, unscrupulous, vulpine, wary, wily