Rancid comes from Latin rancidus ('stinking, rank'), from rancere ('to be rotten or stink'). The historical chain includes Latin rancidus and Latin rancere. Older glosses in the chain include "stinking, rank" and "to be rotten or stink", which help explain the semantic range of the modern word. Morphologically, rancid is best read as borrowing, yielding an English adjective shaped by both form history and later usage. In current English it functions as an adjective, with the sense "smelling or tasting unpleasantly stale, as of spoiled fat or oil". English derivatives include rancidity and rancidness; related forms include rancor. The result is an English adjective whose etymology preserves the older forms while supporting the word's specialized modern meaning.