Etymology

Originated in Latin as Vulgaris Ærae (vulgaris from vulgus: "the common people", ie. those who are not royalty) at least as early as 1615, long before vulgar came to mean "crudely indecent".

A 1635 English edition of a book written by Kepler has the title page in English, and is, so far, the earliest-found usage of Vulgar Era in English.

A 1716 book in English by Dean Humphrey Prideaux says, "before the beginning of the vulgar æra, by which we now compute the years from his incarnation."

The English phrase "common Era" appears at least as early as 1715 in a book on astronomy, used synonymously with "Christian Era" and "Vulgar Era".

The phrase "common era" was used as an English synonym for "vulgar era" again in 1770, in a translation of a book originally written in German.
The 1797 edition of the Encyclopedia Britannica uses the terms vulgar era and common era synonymously.

The term was later mentioned in Alexander Campbell's 1835 book Living Oracles: "The vulgar Era, or Anno Domini; the fourth year of Jesus Christ, the first of which was but eight days." In its article on General Chronology, the 1908 Catholic Encyclopedia stated that "Foremost among these (dating eras) is that which is now adopted by all civilized peoples and known as the Christian, Vulgar or Common Era, in the twentieth century of which we are now living."

Proper noun

1. the method of numbering years whereby the current internationally recognized year is on the Gregorian calendar; secular equivalent of anno Domini and the Christian Era.