false vs faithlessly

false is an adjective but faithlessly is not an adjective.

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

As adverbs, false and faithlessly are synonyms defined as:

Other synonyms of false include traitorously, treacherously, treasonably.

false (adjective)	faithlessly (adjective)
not in accordance with the fact or reality or actuality
not genuine or real; being an imitation of the genuine article
adopted in order to deceive
designed to deceive
(used especially of persons) not dependable in devotion or affection; unfaithful
arising from error
inaccurate in pitch
deliberately deceptive
erroneous and usually accidental
inappropriate to reality or facts

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