cod (n.)

large sea fish, edible and widely distributed in colder seas, mid-14c. (late 13c. in a surname, Thomas cotfich), of unknown origin; despite similarity of form it has no conclusive connection to the widespread Germanic word for "bag" (represented by Old English codd, preserved in codpiece). Codfish is from 1560s. Cod-liver oil, known at least since 1610s, was recommended medicinally from 1783 but did not become popular as a remedy until after 1825.