eponym

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A word or name derived from the name of a person. The words atlas, bowdlerize, and Turing machine are eponyms.
2. n. A person whose name is or is thought to be the source of the name of something.

Century Dictionary and Cyclopedia

1. n. A name of a place, people, or period derived from that of a person.
2. n. A name of a mythical or historical personage from whom the name of a country or people has come or is supposed to have come: thus, Italus, Romulus, Brutus, Heber, the names of imaginary persons invented to account for Italy, Rome, Britain, Hebrew, are mythical eponyms; Bolivar is the historical eponym of Bolivia.
3. n. A name of something, as a part or organ of the body, derived from a person: thus, circle of Willis, fissure of Sylvius, aqueduct of Fallopius, are eponyms.
4. n. The archon eponymus at Athens (see archon); also, one of certain Assyrian functionaries who gave their names to the years during which they held office.

Wiktionary

1. n. The name of a real or fictitious person whose name has, or is thought to have, given rise to the name of a particular item.
2. n. A word formed from a real or fictive person’s name.

GNU Webster's 1913

1. n. The hypothetical individual who is assumed as the person from whom any race, city, etc., took its name.
2. n. A name, as of a people, country, and the like, derived from that of an individual.

WordNet 3.0

1. n. the name derived from a person (real or imaginary)
2. n. the person for whom something is named