Eponymous
Etymology
From Greek "epōnumos," "given as a name," built from "epi" ("upon") and "onoma" ("name"). It entered English through classical scholarship, where an eponymous hero was the ancestor a city or tribe was named for. The two modern uses — the namesake person and the self-titled work — both descend directly from that root idea of a name laid upon something.
adjective · /ih-PON-uh-mus/
Being the person or thing that something else is named after — or, of a work, sharing its title with its main subject.
What it names
The precise word for the relationship of naming: reach for it when a band’s first album is called by the band’s own name, or when a character lends their name to the whole book.
Example
The diner’s eponymous owner, Sal, still worked the grill at seventy.
Related idea
Compare namesake, which points the other way: a namesake is the thing named after someone, while the eponymous figure is the one doing the naming.