Synonyms and related words :
artful, back-door, backstairs, calculating, chiseling, clandestine, collusive, conspiratorial, covert, covinous, crafty, cunning, deceitful, doggo, FALSE, falsehearted, feline, finagling, foxy, fraudulent, guileful, hidden, hidden out, hidlings, hole-and-corner, hugger-mugger, in ambush, in hiding, in the wings, indirect, insidious, lurking, on tiptoe, private, privy, prowling, pussyfoot, pussyfooted, quiet, scheming, secret, secretive, sharp, shifty, skulking, slinking, slinky, slippery, sly, sneaking, sneaky, stealing, stealthy, surreptitious, treacherous, trickish, tricky, two-faced, under cover, under the table, under-the-counter, under-the-table, undercover, underground, underhand, underhanded, unobtrusive, untrustworthy, waiting concealed, wily