noun, a cleaning or emulsifying agent made by reacting animal or vegetable fats or oils with potassium or sodium hydroxide. Soaps often contain colouring matter and perfume and act by emulsifying grease and lowering the surface tension of water, so that it more readily penetrates open materials such as textiles. See also detergent. Related adj saponaceous

From Collins

©HarperCollins 2008. Collins English Dictionary definition of soap