faithlessly vs treacherously

faithlessly and treacherously both are adverbs.

Word	Noun	Adjective	Verb	Adverb
faithlessly	No	No	No	Yes
treacherously	No	No	No	Yes

As adverbs, faithlessly and treacherously are synonyms defined as:

Other synonyms of faithlessly include false, traitorously, treasonably.

faithlessly (adverb)	treacherously (adverb)
in a disloyal and faithless manner	in a disloyal and faithless manner