1 adverb in deceit, betrayalgo fealltachle feallgo cealgach c m uhe was treacherously killedmaraíodh go fealltach é2 adverb dangerouslygo contúirteach c m uthe rocks are treacherously slipperytá na carraigeacha thar a bheith sleamhain agus contúirteachthe road was treacherously icybhí oighear ar an mbóthar a d'fhág an-chontúirteach é