Tonic Water: Binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade; widely used as a solvent. The part of the earth's surface covered with water (such as a river or lake or ocean). Once thought to be one of four elements composing the universe (empedocles). A facility that provides a source of water. Liquid excretory product. A liquid necessary for the life of most animals and plants.