as yet vs hitherto

as yet and hitherto both are adverbs.

Word	Noun	Adjective	Verb	Adverb
as yet	No	No	No	Yes
hitherto	No	No	No	Yes

As adverbs, as yet and hitherto are synonyms defined as:

as yet and hitherto: used in negative statement to describe a situation that has existed up to this point or up to the present time

Other synonyms of as yet include heretofore, so far, thus far, til now, until now, up to now, yet.

as yet (adverb)	hitherto (adverb)
used in negative statement to describe a situation that has existed up to this point or up to the present time	used in negative statement to describe a situation that has existed up to this point or up to the present time