GILL

also spelled jill, in measurement, unit of volume in the British Imperial and U.S. Customary systems. It is used almost exclusively for the measurement of liquids. Although its capacity has varied with time and geography, in the United States it is defined as half a cup, or four U.S. fluid ounces, which equals 7.219 cubic inches, or 118.29 cubic cm; in Great Britain the gill is five British fluid ounces, which equals 8.669 cubic inches, or 142.07 cubic cm. The gill was introduced in the 13th century to measure individual servings of wine. The term jill appears in the nursery rhyme Jack and Jill. When Charles I of England scaled down the jack (at that time a two-ounce measure) so as to collect higher sales taxes, the jill, by definition twice the size of the jack, was automatically reduced also and came tumbling after. in biology, type of respiratory organ found in many aquatic animals, including a number of worms, nearly all mollusks and crustaceans, some insect larvae, all fishes, and a few amphibians. The gill consists of branched or feathery tissue richly supplied with blood vessels, especially near the gill surface, facilitating the exchange of oxygen and carbon dioxide with the surrounding water. The gills may be enclosed in cavities, through which the water is often forcibly pumped, or they may project from the body into the water.