The act of uniting or the state of being united. A combination so formed, especially an alliance or confederation of people, parties, or political entities for mutual interest or benefit. Mathematics A set, every member of which is an element of one or another of two or more given sets. Agreement or harmony resulting from the uniting of individuals; concord. The state of matrimony; marriage: "The element that was to make possible such a union was trust in each other's love\u201d ( Kate Chopin). Sexual intercourse. A combination of parishes for joint administration of relief for the poor in Great Britain. A workhouse maintained by such a union. A labor union. A coupling device for connecting parts, such as pipes or rods. A device on a flag or ensign, occupying the upper inner corner or the entire field, that signifies the union of two or more sovereignties. An organization at a college or university that provides facilities for recreation; a student union. A building housing such facilities. The United States of America regarded as a national unit, especially during the Civil War. Of, relating to, or loyal to the United States of America during the Civil War: a Union soldier. Of or relating to a labor union or labor union organizing: the union movement; union negotiations.