Gruel is a food consisting of some type of cereal—such as ground oats, wheat, rye or rice—boiled in water or milk. It is a thinner version of porridge that may be more often drunk rather than eaten and may not need to be cooked. Historically, gruel has been a staple of the Western diet, especially for peasants. Gruel is often made from millet, hemp, barley, or, in hard times, from chestnut flour or even the less bitter acorns of some oaks. Gruel is also a colloquial expression for any watery or liquidy food of unknown character, e.g., pea soup.