langsyne vs past

langsyne and past both are nouns.

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

As nouns, past is a hypernym of langsyne; that is, past is a word with a broader meaning than langsyne:

Other hypernyms of langsyne include past times, yesteryear.

langsyne (noun)	past (noun)
past times remembered with nostalgia	a verb tense that expresses actions or states in the past
	the time that has elapsed
	a earlier period in someone's life (especially one that they have reason to keep secret)

langsyne (adjective)	past (adjective)
	earlier than the present time; no longer current
	of a person who has held and relinquished a position or office

langsyne (adverb)	past (adverb)
of the distant or comparatively distant past	so as to pass a given point