1. (a.) Lying in wait; working quietly to ensnare or entrap; as, insidious rumors\.

2. (a.) Intended to entrap; characterized by treachery and deceit; as, insidious arts.

Byzantine Machiavellian Machiavellic acute amoral arch artful astute cagey calculating canny chiseling clever collusive conscienceless corrupt corrupted covinous crafty criminal crooked cunning cute dangerous dark deceitful deep deep-laid designing devious diplomatic dishonest dishonorable doubtful dubious evasive FALSE falsehearted feline felonious finagling fishy foxy fraudulent furtive gradual guileful ill-got ill-gotten immoral indirect ingenious inventive knowing not kosher pawky perfidious perilous politic questionable ready resourceful rotten scheming serpentine shady shameless sharp shifty shrewd sinister slick slippery sly smooth snaky sneaky sophistical stealthy strategic subtile subtle supple surreptitious suspicious tactical treacherous trickish tricksy tricky two-faced unconscienced unconscientious unconscionable underhand underhanded unethical unprincipled unsavory unscrupulous unstraightforward vulpine wary wily without remorse without shame