Adverb
in a disloyal and faithless manner
Source: WordNetDrunkenness is the vice of a good constitution or of a bad memory-of a constitution so treacherously good that it never bends till it breaks; or of a memory that recollects the pleasures of getting intoxicated, but forgets the pains of getting sober. Charles Caleb Colton
And in that place the cruel tyrant, Love, Who treacherously every promise breaks, Who bides his time and watches every move, And every chance to thwart true lovers takes. Ludovico Ariosto
On board all vessels at sea and in port, and at our many island bases in the Pacific, there is rejoicing and thanksgiving. The long and bitter struggle, which Japan started so treacherously on the 7th of December 1941, is at an end. Chester W. Nimitz
Have we not all one Father? Has not one God created us? Why do we deal treacherously with one another By profaning the covenant of the fathers? Malachi
he behaved treacherously Source: Internet
his wife played him false Source: Internet