eponym

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A word or name derived from a proper noun. The words atlas, bowdlerize, denim, and Turing machine are eponyms.
• noun One whose name is or is thought to be the source of the name of something.

from The Century Dictionary.

• noun 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.
• noun A name of a place, people, or period derived from that of a person.
• noun 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.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

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

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• noun A word formed from a real or fictive person’s name.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the name derived from a person (real or imaginary)
• noun the person for whom something is named