Vestigial

vɛˈstɪdʒiəl

adjective

forming a very small remnant of something that was once much larger or more noticeable

The term 'vestigial' is often used in biology to describe organs or structures that have lost most or all of their original function in the course of evolution. These vestigial remnants offer clues to an organism's evolutionary history.

See how Haruki Murakami uses "vestigial", with its meaning, pronunciation and a real book example.