treacherously russian

• преда́тельски

  treacherously, perfidiously, deceitfully

• коварно

  insidiously, treacherously, perfidiously, craftily

• изме́ннически

  treacherously, traitorously, perfidiously

Examples

• И сказа́л я: беда́ мне, беда́ мне! увы мне! злоде́и злоде́йствуют, и злоде́йствуют злоде́и злоде́йски.

  And I said, My leanness, my leanness, woe unto me! The treacherous have dealt treacherously; yea, the treacherous have dealt very treacherously.

• Он коварно обманул своего лучшего друга.

  He treacherously deceived his best friend.