Rarefacere

Part of speech: verb

Definitions

1. To make something less dense or more rare
2. to create a condition where something becomes thinner or less concentrated
3. to reduce the frequency or abundance of a substance or phenomenon

Etymology: "Rarefacere" is a Latin verb meaning "to make thin," built from "rarus" ("thin, sparse, loose in texture") and "facere" ("to make, do"). The sense of thinning gave English its "rarefy," which describes air becoming thinner at high altitude or a substance losing density, and in older usage it could also describe a crowd or population becoming less dense. The Latin root "rarus" is also the source of English "rare," which once meant only "thin" or "loosely spaced" before acquiring its modern sense of "uncommon." The two words share a single ancestor, so a rare thing and a rarefied thing both began as things with gaps between their parts.