lang syne vs langsyne

lang syne and langsyne both are nouns.

Word	Noun	Adjective	Verb	Adverb
lang syne	Yes	No	No	Yes
langsyne	Yes	No	No	Yes

As nouns, lang syne and langsyne are synonyms defined as:

Other synonyms of lang syne include auld langsyne, good old days, old times.

As adverbs, lang syne and langsyne are synonyms defined as:

Other synonyms of lang syne include long ago, long since.

lang syne (noun)	langsyne (noun)
past times remembered with nostalgia	past times remembered with nostalgia

lang syne (adverb)	langsyne (adverb)
of the distant or comparatively distant past	of the distant or comparatively distant past