Of or pertaining to a vestige or remnant; like a vestige.

Nonfunctioning, a remnant of a body part that existed in a former species of an animal. Whales have tiny, vestigial hind legs buried deep in their bodies.

In the nature of a vestige or remnant.

remnant or relict of. (example: "vestigial webbing" is with only a trace of webbing).

Pertaining to part of an animal that is in the process of being evolutionarily lost and is small, imperfectly formed, and serves no function.