The Collaborative International Dictionary of English v.0.48:

Era \E"ra\, n.; pl. Eras. [LL. aera an era, in earlier usage,
   the items of an account, counters, pl. of aes, aeris, brass,
   money. See Ore.]
   1. A fixed point of time, usually an epoch, from which a
      series of years is reckoned.
      [1913 Webster]

            The foundation of Solomon's temple is conjectured by
            Ideler to have been an era.           --R. S. Poole.
      [1913 Webster]

   2. A period of time reckoned from some particular date or
      epoch; a succession of years dating from some important
      event; as, the era of Alexander; the era of Christ, or the
      Christian era (see under Christian).
      [1913 Webster]

            The first century of our era.         --M. Arnold.
      [1913 Webster]

   3. A period of time in which a new order of things prevails;
      a signal stage of history; an epoch.
      [1913 Webster]

            Painting may truly be said to have opened the new
            era of culture.                       --J. A.
                                                  Symonds.

   Syn: Epoch; time; date; period; age; dispensation. See
        Epoch.
        [1913 Webster]

WordNet (r) 3.0 (2006):

era
    n 1: a period marked by distinctive character or reckoned from a
         fixed point or event [syn: era, epoch]
    2: a major division of geological time; an era is usually
       divided into two or more periods [syn: era, geological
       era]
    3: (baseball) a measure of a pitcher's effectiveness; calculated
       as the average number of earned runs allowed by the pitcher
       for every nine innings pitched [syn: earned run average,
       ERA]

The Free On-line Dictionary of Computing (19 January 2023):

ERA

   Entity-Relationship-Attribute


The Free On-line Dictionary of Computing (19 January 2023):

era

   Synonym epoch.  Webster's Unabridged makes these words
   almost synonymous, but "era" usually connotes a span of time
   rather than a point in time.


The Jargon File (version 4.4.7, 29 Dec 2003):

era
 n.

    Syn. epoch. Webster's Unabridged makes these words almost synonymous, but
    era more often connotes a span of time rather than a point in time, whereas
    the reverse is true for epoch. The epoch usage is recommended.