An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include eponymous and eponymic.
Usage of the word
The term eponym functions in multiple related ways, all based on an explicit relationship between two named things. A person, place, or thing named after a particular person share an eponymous relationship. In this way, Elizabeth I of England is the eponym of the Elizabethan era, but the Elizabethan era can also be referred to as the eponym of Elizabeth I of England.
When Henry Ford is referred to as "the eponymous founder of the Ford Motor Company", his surname "Ford" and the name of the motor company have an eponymous relationship. The word "eponym" can also refer to the title character of a fictional work (such as Rocky Balboa of the Rocky film series), as well as to self-titled works named after their creators (such as the album The Doors by the band the Doors).
Walt Disney created the eponymous Walt Disney Company, with his name similarly extended to theme parks such as Walt Disney World. Medical eponymous terms are often called medical eponyms although that usage is deprecable.
History
Periods have often been named after a ruler or other influential figure: One of the first recorded cases of eponymy occurred in the second millennium BC, when the Assyrians named each year after a high official (limmu). In ancient Greece, the eponymous archon was the highest magistrate in classical Athens. Eponymous archons served a term of one year which took the name of that particular archon (e.g., 594 BC was named after Solon). Later historians provided yet another case of eponymy by referring to the period of fifth-century Athens as The Age of Pericles after its most influential statesman Pericles. In Ptolemaic Egypt, the head priest of the Cult of Alexander and the Ptolemies was the eponymous priest after whom years were named. 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 (Cain's life is detailed in Gen. 4:1-16)) are said to be named after 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). Government administrations may become referred to eponymously, such as Kennedy's Camelot and the Nixon Era. British monarchs have become eponymous throughout the English-speaking world for time periods, fashions, etc. Elizabethan, Georgian, Victorian, and Edwardian are examples of these.
Trends
Political trends or movements are often eponymously named after a government leader. Examples include Jacksonian democracy, Stalinism, Maoism, Obamacare, and Thatcherism.