era vs Common era

era and Common era both are nouns.

Word	Noun	Adjective	Verb	Adverb
era	Yes	No	No	No
Common era	Yes	No	No	No

era (noun)	Common era (noun)
a period marked by distinctive character or reckoned from a fixed point or event	the time period beginning with the supposed year of Christ's birth
a major division of geological time; an era is usually divided into two or more periods