sperm oil, liquid wax obtained from the sperm whale, or cachalot, and related marine mammals. It flows readily, is clear, and varies in color from pale yellow to brownish yellow. Chemically it is not a true oil. It is secured from the blubber and from a huge cavity in the whale's head (this oil cavity helps the whale keep part of his head above water for breathing). A solid wax, spermaceti, is extracted from the oil by filtration and treatment with potassium hydroxide. The oil is an excellent lubricant, especially for watches and other delicate instruments, and is used as a dressing for leather, to protect plants from insects, in tempering steel, and in making soap.

whale oil, oil extracted from the blubber and other parts of certain species of whales. It varies in composition, color, and the degree of fishy odor according to the method and extent of refining. Formerly widely used as an illuminant, it was superseded by petroleum products. It is used today in soapmaking, as a leather dressing, and as a lubricant. Some is hydrogenated to form edible fats. The term is also sometimes used to include sperm oil.