Tunicin

Part of speech: noun

Definitions

1. A cellulose-like compound that forms the outer covering or tunic of marine animals called tunicates
2. A structural polysaccharide found in the protective layer surrounding the bodies of sea squirts and other tunicates
3. A carbohydrate polymer chemically similar to cellulose that comprises the tough outer sheath of tunicate organisms

Etymology: Tunicin is a chemical name built from "tunic" and the suffix "-in," which chemists use to name substances, especially proteins and other compounds isolated from a source. The tunic in question is the outer covering of sea squirts (tunicates), the marine animals whose body wall is a leathery sheath made largely of cellulose-like material. Naming the protein or compound after the tunic it came from is a direct, almost literal bit of scientific labeling. The formation itself is plain: a common English noun, with the chemical suffix attached to mark it as a substance rather than a garment or a body part. Nothing in the word's history involves a shift in meaning, so its interest lies in how it turns an everyday word for clothing into a label for something found in the sea.