Eponym and its more-popular adjective, eponymous, refer to the person, place, or thing that lends its name to something else; namesake is the something else that bears the eponym’s name. Thus The eponymous hero is best remembered through the Orion constellation and The Bordeux region is the eponym of one of my favorite wines. Do not call a namesake an eponym, an unfortunately-common error that may lead to confusion: Prefer James Joyce’s Ulysses moves the Greek hero Odysseus into modern Dublin to James Joyce’s eponymous novel moves the Greek hero Odysseus into modern Dublin, which suggests the novel is called either James Joyce or Odysseus.