Olympiad vs period of time

Olympiad and period of time both are nouns.

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

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

Olympiad: one of the four-year intervals between Olympic Games; used to reckon time in ancient Greece for twelve centuries beginning in 776 BC
period of time: an amount of time

Other hypernyms of Olympiad include period, time period.

Olympiad (noun)	period of time (noun)
the modern revival of the ancient games held once every 4 years in a selected country	an amount of time
one of the four-year intervals between Olympic Games; used to reckon time in ancient Greece for twelve centuries beginning in 776 BC