Terpin

Part of speech: noun

Definitions

1. A crystalline chemical compound, usually taken as terpin hydrate, used to loosen phlegm in coughs
2. A terpene-derived crystalline substance, often prescribed as an expectorant to ease chesty coughing
3. An organic compound obtained from turpentine oil, valued in medicine as a mucus-thinning cough remedy

Etymology: Terpin is a chemical name built from the word "turpentine" and a chemical suffix. The substance is named after the tree resin it comes from: turpentine, the volatile oil distilled from pine resin, gave its name to the family of hydrocarbons called terpenes, and "terpin" is a derivative of that family. The suffix "-in" is the standard chemical ending used for many neutral organic compounds, so the name records both the source of the material and the chemical class it belongs to. The shorter form "terp-" in the word is the stem of "terpene," which was itself formed from "turpentine" by cutting it down to its core. That makes "terpin" and "terpene" what etymologists call piecewise doublets: two words that share the same stem and grew from the same origin, but were built separately rather than one descending from the other.