Synonyms for Insidiously:

• adv.

  •all (adverb)
  • insidiously.
  •secretly (adverb)
  • by stealth,
  • in strict confidence,
  • in confidence,
  • behind someone's back,
  • under the table,
  • privily,
  • behind closed doors,
  • on the qt,
  • obscurely,
  • in secret,
  • personally,
  • in holes and corners,
  • in camera,
  • confidentially,
  • sub rosa,
  • unobserved,
  • on the sly,
  • quietly,
  • hush-hush,
  • on the quiet,
  • intimately.
  •slyly (adverb)
  • intelligently,
  • shrewdly.

• Other synonyms:

  •Other relevant words:
  • perfidiously,
  • guilefully,
  • back,
  • traitorously,
  • privately,
  • covertly,
  • elusively,
  • sneakily,
  • artfully,
  • clandestinely,
  • treacherously,
  • banefully,
  • underhandedly,
  • fraudulently,
  • falsely,
  • designingly,
  • subtly,
  • surreptitiously,
  • snakily,
  • furtively,
  • huggermugger,
  • deceptively,
  • deceitfully,
  • stealthily,
  • underhand,
  • smoothly,
  • slick,
  • tortuously,
  • Infamously,
  • shiftily,
  • disingenuously,
  • knowingly,
  • indirectly,
  • faithlessly,
  • harmfully,
  • deviously,
  • slimly.

Antonyms for Insidiously:

• adv.

  • secretly
    openly, publicly.