- era, geological era - a major division of geological time; an era is usually divided into two or more periods
--1 is a kind of geological time, geologic time
--1 is a part of eon, aeon
--1 has parts: period, geological period
--1 has particulars:Cenozoic, Cenozoic era, Age of Mammals; Mesozoic, Mesozoic era, Age of Reptiles; Paleozoic, Paleozoic era