(n.) Like a sneak; sneaking.

Machiavellian Machiavellic acute arch artful astute back-door backstairs cagey calculating canny chiseling clandestine clever collusive covert covinous cowering crafty cringing cunning cute deceitful deep deep-laid designing devious diplomatic dishonest disingenuous duplicitous FALSE falsehearted feline finagling foxy fraudulent furtive guileful hidlings hole-and-corner hugger-mugger indirect ingenious insidious inventive knowing pawky politic privy quailing quiet ready resourceful scheming serpentine sharp shifty shrewd skulking slick slinking slinky slippery sly smooth snaky sneaking sophistical stealthy strategic subtile subtle supple surreptitious tactical treacherous trickish tricksy tricky two-faced under-the-counter under-the-table undercover underground underhand underhanded unobtrusive unscrupulous vulpine wary wily