1. a. The act of uniting or the state of being united. b. A combination so formed, especially an alliance or confederation of people, parties, or political entities for mutual interest or benefit.

2. Mathematics. A set, every member of which is an element of one or another of two or more given sets.

3. Agreement or harmony resulting from the uniting of individuals; concord. See synonyms at unity.

4. a. The state of matrimony; marriage: "The element that was to make possible such a union was trust in each other's love" (Kate Chopin). b. Sexual intercourse.

5. a. A combination of parishes for joint administration of relief for the poor in Great Britain. b. A workhouse maintained by such a union.

6. A labor union.

7. A coupling device for connecting parts, such as pipes or rods.

8. A device on a flag or an ensign, occupying the upper inner corner or the entire field, that signifies the union of two or more sovereignties.

9. Often Union a. An organization at a college or university that provides facilities for recreation; a student union. b. A building housing such facilities.

10. Union The United States of America regarded as a national unit, especially during the Civil War.

1. Union Of, relating to, or loyal to the United States of America during the Civil War: a Union cause; a Union soldier.

2. Of or relating to a labor union or labor union organizing: the union movement; union negotiations.