Pepsin

n. enzyme found in gastric juices; medication containing the pepsin enzyme

Pepsin is a digestive protease  released by the chief cells in the stomach that functions to degrade food proteins into peptides. According to American Heritage Dictionary, pepsin derives from the Greek word pepsis, meaning digestion (peptein: to digest). Pepsin was discovered by Theodor Schwann in 1836. It was the first animal enzyme to be discovered.
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n. pepsin, enzyme found in gastric juices; medication containing the pepsin enzyme

n. pepsin

(n.)
An unorganized proteolytic ferment or enzyme contained in the secretory glands of the stomach. In the gastric juice it is united with dilute hydrochloric acid (0.2 per cent, approximately) and the two together constitute the active portion of the digestive fluid. It is the active agent in the gastric juice of all animals.