an extended period of years reckoned from a fixed point in time
the Christian era
a historical period begun or typified by some distinctive figure or characteristic feature
the era of space flight
a major division of geological time that is subdivided into periods
the Mesozoic era
a stage in the development of somebody or something
[late Latin aera a number or time used as a basis of reckoning, from Latin, counters, pl of aer-, aes copper, money]