era vs historic period

era and historic period both are nouns.

Word	Noun	Adjective	Verb	Adverb
era	Yes	No	No	No
historic period	Yes	No	No	No

As nouns, historic period is a hyponym of era; that is, historic period is a word with a more specific, narrower meaning than era:

era: a period marked by distinctive character or reckoned from a fixed point or event
historic period: an era of history having some distinctive feature

Other hyponyms of era include day, age, modern era.

era (noun)	historic period (noun)
a period marked by distinctive character or reckoned from a fixed point or event	an era of history having some distinctive feature
a major division of geological time; an era is usually divided into two or more periods