sly

sly, cunning, crafty, wily, tricky, foxy, artful, slick mean attaining or seeking to attain one's ends by guileful or devious means.

sly implies furtiveness, lack of candor, and skill in concealing one's aims and methods.

cunning suggests the inventive use of sometimes limited intelligence in overreaching or circumventing.

crafty implies cleverness and subtlety of method.

wily implies skill and deception in maneuvering.

tricky is more likely to suggest shiftiness and unreliability than skill in deception and maneuvering.

foxy implies a shrewd and wary craftiness usually involving devious dealing.

artful implies indirectness in dealing and often connotes sophistication or cleverness.

slick emphasizes smoothness and guile.