- era, epoch - a period marked by distinctive character or reckoned from a fixed point or event
--1 is a kind of time period, period of time, period
--1 has particulars:Caliphate; Christian era, Common era; day; historic period, age; modern era - era, geological era - a major division of geological time; an era is usually divided into two or more periods
--2 is a kind of geological time, geologic time
--2 is a part of eon, aeon
--2 has parts: period, geological period
--2 has particulars:Cenozoic, Cenozoic era, Age of Mammals; Mesozoic, Mesozoic era, Age of Reptiles; Paleozoic, Paleozoic era