An eponym is a person, place, or thing after whom or after which something is named, or believed to be named. The adjectives derived from eponym include eponymous and eponymic. For example, Elizabeth I of England is the eponym of the Elizabethan era, and "the eponymous founder of the Ford Motor Company" refers to Henry Ford. Recently, especially in the recorded-music industry, eponymous has been used to mean "named after its central character or creator".
The Hebrew Bible explains the origins of peoples through individuals who bear their name. Jacob is renamed "Israel" (Gen 35:9) and his sons (or grandsons) name the original 12 tribes of Israel, while Edomites (Gen. 25:30), Moabites and Ammonites (Gen. 19:30-38), Canaanites (Gen. 9:20-27) and other tribes (the Kenites named after Cain Gen. 4:1-16) are said to be named for other primal ancestors bearing their name. In most cases, the experiences and behavior of the ancestor is meant to indicate the characteristics of the people who take their name.
In ancient Rome, one of the two formal ways of indicating a year was to cite the two annual consuls who served in that year. For example, the year we know as 59 BC would have been described as "the consulship of Marcus Calpurnius Bibulus and Gaius Julius Caesar" (although that specific year was known jocularly as "the consulship of Julius and Caesar" because of the insignificance of Caesar's counterpart). Under the empire, the consuls would change as often as every two months, but only the two consuls at the beginning of the year would lend their names to that year.
During the Christian era, itself eponymous, many royal households used eponymous dating by regnal years. The Roman Catholic Church, however, eventually used the Anno Domini dating scheme based on the birth of Christ on both the general public and royalty. The regnal year standard is still used with respect to statutes and law reports published in some parts of the United Kingdom and in some Commonwealth countries (England abandoned this practice in 1963): a statute signed into law in Canada between February 6, 1994 and February 5, 1995 would be dated 43 Elizabeth II, for instance.
Government administrations may become referred to eponymously, such as Kennedy's Camelot and the Nixon Era.