Synonyms for On the quiet:

• adj.

  •clandestine (adjective)
  • closet,
  • illicit,
  • stealthy,
  • covert,
  • private,
  • illegitimate,
  • sneaky,
  • concealed,
  • hush-hush,
  • furtive,
  • hidden,
  • cloak-and-dagger,
  • underground,
  • fraudulent,
  • artful.
  •underhand (adjective)
  • oblique,
  • guileful,
  • unscrupulous,
  • shifty,
  • sly,
  • devious,
  • indirect,
  • underhanded,
  • two-faced,
  • dishonorable,
  • sub-rosa,
  • lubricious,
  • two-timing,
  • slippery,
  • insidious,
  • treacherous,
  • secretive,
  • dishonest,
  • dirty-dealing,
  • double-crossing,
  • unfair,
  • crooked,
  • sneaking,
  • tricky,
  • wily,
  • unethical,
  • crafty,
  • dirty dealing,
  • duplicitous,
  • cunning,
  • unjust,
  • shady,
  • deceptive.

• adv.

  •covertly (adverb)
  • privately,
  • on the qt,
  • by stealth,
  • stealthily,
  • clandestinely,
  • sub rosa,
  • wildcat,
  • on the sly,
  • in camera,
  • surreptitiously,
  • furtively.
  •secretly (adverb)
  • privily,
  • quietly,
  • unobserved,
  • in confidence,
  • personally,
  • underhandedly,
  • obscurely,
  • in secret,
  • behind closed doors,
  • intimately,
  • in strict confidence,
  • insidiously,
  • behind someone's back,
  • under the table.

• n.

  •confidentially (noun)
  • confidentially.
  •hugger mugger (noun)
  • hugger mugger.
  •secret (noun)
  • secret.

• Other synonyms:

  •cleverly
  • slyly.

Antonyms for On the quiet:

• adj.

  • clandestine
    honest, authorized, known, legal, truthful, open, aboveboard, public, forthright.
  • underhand
    frank.

• adv.

  • covertly
    frankly, honestly, candidly, openly, Overtly, publicly.