Synonyms for Underhandedly:

• adv

  •dishonestly (adverb)
  • untruthfully.
  •falsely (adverb)
  • behind ones back.
  •Other relevant words: (adverb)
  • immensely,
  • out of proportion,
  • illegally,
  • overmuch,
  • extravagantly,
  • disproportionately,
  • inordinately,
  • secretly,
  • immoderately,
  • falsely,
  • indecorously,
  • overfull,
  • unduly.

• adv.

  •dishonestly (adverb)
  • dishonestly,
  • unscrupulously,
  • feloniously,
  • deceitfully,
  • corruptly,
  • fraudulently,
  • treacherously,
  • craftily,
  • traitorously,
  • insincerely,
  • immorally,
  • hypocritically,
  • deviously,
  • dishonorably,
  • crookedly.
  •falsely (adverb)
  • malevolently,
  • disloyally,
  • perfidiously,
  • unfaithfully,
  • maliciously,
  • basely,
  • behind one's back,
  • falseheartedly,
  • faithlessly,
  • roguishly.
  •overmuch (adverb)
  • excessively.
  •secretly (adverb)
  • personally,
  • intimately,
  • hush-hush,
  • on the quiet,
  • sub rosa,
  • unobserved,
  • behind closed doors,
  • in strict confidence,
  • in secret,
  • under the table,
  • behind someone's back,
  • on the qt,
  • privately,
  • by stealth,
  • privily,
  • in confidence,
  • obscurely,
  • in camera,
  • confidentially,
  • in holes and corners.
  •unduly (adverb)
  • overly,
  • too,
  • extremely,
  • unjustifiably,
  • over,
  • improperly,
  • unnecessarily,
  • unreasonably,
  • unjustly,
  • ever,
  • unfairly.
  •untruthfully (adverb)
  • untruly,
  • wrongly,
  • deceivingly,
  • mendaciously.

• n.

  •Other relevant words: (noun)
  • trickily,
  • underhand,
  • slyly,
  • sneakily.

• Other synonyms:

  •Other relevant words (noun):
  • on the side,
  • Slily,
  • on the sly,
  • disingenuously,
  • deceptively,
  • questionably,
  • indirectly,
  • surreptitiously,
  • furtively,
  • stealthily,
  • quietly,
  • foully,
  • Infamously,
  • guilefully,
  • sly,
  • irregularly,
  • clandestinely,
  • underarm,
  • covertly,
  • Hiddenly,
  • insidiously,
  • shiftily.

Antonyms for Underhandedly:

• adv.

  • falsely
    truthfully, honestly.
  • secretly
    publicly, openly.
  • unduly
    justly, fairly, reasonably, moderately, sensibly.