spermaceti, solid waxy substance, white, odorless, and tasteless, separated from the oils obtained from the sperm whale (see sperm oil) and other marine mammals. A mixture of esters of fatty acids, it is composed chiefly of cetyl palmitate. Spermaceti is insoluble in water and does not putrefy. It is used mostly in ointments and cosmetics and in fine candles and was widely employed formerly as the waterproofing medium for oilskins.