langsyne vs auld langsyne

langsyne and auld langsyne both are nouns.

Word	Noun	Adjective	Verb	Adverb
langsyne	Yes	No	No	Yes
auld langsyne	Yes	No	No	No

As nouns, langsyne and auld langsyne are synonyms defined as:

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

langsyne (noun)	auld langsyne (noun)
past times remembered with nostalgia	past times remembered with nostalgia

langsyne (adverb)	auld langsyne (adverb)
of the distant or comparatively distant past