Definition -
(1) A word that has been created from someone's name (e.g. the word martinet was derived from the name Marquis de Martinet [a Frenchman]).
(2) A person from whose name an eponym has been created (e.g. the Marquis de Martinet himself).

Etymology -
The word eponym was coined by contracting the word eponymous, which derives from the Greek eponymos, the giving of one's name to a thing (from Greek epi, upon + onyma, name).

Oxford English Dictionary -
Its first citation is from 1846:
"Pelops is the eponym or name-giver of the Peloponnesus."
(Grote Greece i. vii. (1869) I. 150)

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