great year vs time period

great year and time period both are nouns.

Word	Noun	Adjective	Verb	Adverb
great year	Yes	No	No	No
time period	Yes	No	No	No

As nouns, time period is a hypernym of great year; that is, time period is a word with a broader meaning than great year:

great year: time required for one complete cycle of the precession of the equinoxes, about 25,800 years
time period: an amount of time

Other hypernyms of great year include period, period of time.

great year (noun)	time period (noun)
time required for one complete cycle of the precession of the equinoxes, about 25,800 years	an amount of time