historic period vs era

historic period and era both are nouns.

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

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

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

Other hypernyms of historic period include epoch.

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