Dictionary of Ichthyology
cod liver oil = 1) oil extracted by boiling the livers. May be made from other gadoids such as haddock. Once used as a basis for paints, to tan leather, and as a dietary and medicinal supplement as it contained vitamins A and D (tastes awful from long personal experience (BWC) in the 1940s and 1950s when taken in liquid form, only marginally better when encapsulated).