Insidious1. (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.
Thesaurus Entries
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