good old days vs yesteryear

good old days and yesteryear both are nouns.

Word	Noun	Adjective	Verb	Adverb
good old days	Yes	No	No	No
yesteryear	Yes	No	No	No

As nouns, yesteryear is a hypernym of good old days; that is, yesteryear is a word with a broader meaning than good old days:

Other hypernyms of good old days include past, past times.

good old days (noun)	yesteryear (noun)
past times remembered with nostalgia	the time that has elapsed