millenary vs period of time

millenary and period of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
millenary	Yes	Yes	No	No
period of time	Yes	No	No	No

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

Other hypernyms of millenary include period, time period.

millenary (noun)	period of time (noun)
a sum or aggregate of one thousand (especially one thousand years)	an amount of time
a span of 1000 years
the 1000th anniversary (or the celebration of it)

millenary (adjective)	period of time (adjective)
relating to or consisting of 1000
of or relating to the doctrine of the millennium