A namesake is a person or thing named after someone or something else. When your parents name you after your grandfather William, you become his namesake.

You might meet someone who attends Martin Luther King Jr. Elementary School and learn that the school is the namesake of the civil rights leader. When explorers discover a new species of butterfly and name it after a famous biologist, that butterfly becomes her namesake.

Sometimes people use namesake to mean the older person or thing, but that's not quite correct. The person or thing that a namesake is named after is called the eponym. Lake Victoria is the namesake of Queen Victoria, and Queen Victoria is the eponym of Lake Victoria.