Chlorine Chlo"rine, n. [Gr. ? pale green, greenish yellow. So named from its color. See Yellow.] (Chem.) One of the elementary substances, commonly isolated as a greenish yellow gas, two and one half times as heavy as air, of an intensely disagreeable suffocating odor, and exceedingly poisonous. It is abundant in nature, the most important compound being common salt. It is powerful oxidizing, bleaching, and disinfecting agent. Symbol Cl. Atomic weight, 35.4. Chlorine family, the elements fluorine, chlorine, bromine, and iodine, called the halogens, and classed together from their common peculiarities.