insidious (adj.)

• acute
• arch
• artful
• astute
• cagey
• calculating
• canny
• clever
• collusive
• conscienceless
• corrupt
• corrupted
• crafty
• criminal
• crooked
• cunning
• cute
• dangerous
• dark
• deceitful
• deep
• deep-laid
• designing
• devious
• diplomatic
• dishonest
• dishonorable
• doubtful
• dubious
• evasive
• false
• feline
• felonious
• fishy
• foxy
• fraudulent
• furtive
• gradual
• guileful
• ill-gotten
• immoral
• indirect
• ingenious
• inventive
• knowing
• 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
• subtle
• supple
• surreptitious
• suspicious
• tactical
• treacherous
• tricksy
• tricky
• two-faced
• unconscientious
• unconscionable
• underhand
• underhanded
• unethical
• unprincipled
• unsavory
• unscrupulous
• vulpine
• wary
• wily