eponym eponym /ˈɛpənɪm/

noun

1. The name derived from a person (real or imaginary)  ( eponym )
   the name derived from a person (real or imaginary)
    Down's syndrome is an eponym for the English physician John Down
   Down's syndrome is an eponym for the English physician John Down
   
2. The person for whom something is named  ( eponym )
   the person for whom something is named
    Constantine I is the eponym for Constantinople
   Constantine I is the eponym for Constantinople