"epoch" in the noun sense
1. era, epoch
a period marked by distinctive character or reckoned from a fixed point or event
2. epoch, date of reference
astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded
a unit of geological time that is a subdivision of a period and is itself divided into ages
Source: WordNet® (An amazing lexical database of English)
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