A small sea animal that lived hundreds of millions of years ago and died out long before the dinosaurs. Nobody has ever seen a living one — what we have are the fossils, and they are everywhere, which is why the word exists at all. The animal looked a little like a woodlouse or a horseshoe crab: a flat oval body with a hard shell, divided down its length into three long strips, and divided across into many small segments. That lengthwise three-part split is what the name is about. In English the word is used the way a scientific name is used, but ordinary people say it too — museum labels, children's fossil books, rock shops. It is a countable noun (a trilobite, two trilobites), and you will often hear 'a trilobite fossil' even though the fossil is really all that is left. Say it TRY-luh-bite.

三葉蟲（古生代的海洋節肢動物化石，比恐龍還早滅絕）。