Meaning

noun the process of gradually becoming inferior

noun a gradual decrease; as of stored charge or current

noun the organic phenomenon of rotting

originFrom Middle English decaien (“to decrease, diminish”) and decai (“deterioration, decline in value”), from Anglo-Norman decaeir (“to fall away, decay, decline”), from Vulgar Latin *dēcadere, etymologically restored form of Latin dēcidere (“to fall down, to fail, sink or perish”), from de- (“of, from, away, down”) + cadere (“to fall”). Compare decadent and decadence.

Etymology from Wiktionary, CC BY-SA 3.0