lustrum vs period of time

lustrum and period of time both are nouns.

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

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

Other hypernyms of lustrum include period, time period.

lustrum (noun)	period of time (noun)
a ceremonial purification of the Roman population every five years following the census	an amount of time
a period lasting five years