epoch

Definitions:

A fixed point or period of time remarkable for some great event or series of events from which succeeding years, as connected therewith, are numbered; any remarkable period of time; date; the beliocentric longitude of a planet at any given time.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (noun) (n.) (noun)
A point of time, marked by events of great importance; a period of years filled with unusual events.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
A fixed point of time from which succeeding years are numbered; a period in the progress of events when some important occurrence takes place; a fixed and important period of novelty or change; in geol., age or era.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (noun) (n.) (noun)
A point of time fixed or made remarkable by some great event from which dates are reckoned: a period remarkable for important events.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (noun) (n.) (noun)
A remarkable period of time; date from which an era is reckoned.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (noun) (n.) (noun)

Usage examples:

Be that as it may, she opened a new era in the history of my childhood; and, during the six or seven years that followed the epoch of my uncle's marriage, my life was as happy as that of a human creature can be.
- Ellen Middleton--A Tale by Georgiana Fullerton
It is a nice nocturne, neat in its sorrow, yet not epoch making.
- Chopin: The Man and His Music by James Huneker
The Gospels contain the teachings of the Christ of that epoch but the Christs of our time receive other teachings appropriate to the needs of the present day.
- Modern Saints and Seers by Jean Finot