treacherously

adverb

treach·​er·​ous·​ly

: in a treacherous manner : by or with treachery

treacherously wounded by one of the enemy generals who had invited him to a parley

—Robert Graves

doomed … to a wife unworthy of him, just because of … a moon treacherously sentimental

—Donn Byrne

Word History

Etymology

Middle English tricherously, from trecherous, tricherous + -ly

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