noun

1. a uniting or being united; combination; esp.,
   1. a combining, joining, or grouping together of nations, states, political groups, etc. for some specific purpose
   2. a marrying or being married; marriage
2. something united or unified; a whole made up of parts; esp.,
   1. an organization or confederation uniting various individuals, political units, etc.
   2. labor union
   3. in England, a former combination of parishes for the joint administration of relief for the poor; also, a workhouse kept up by such a union
3. a design symbolizing political union, used in a flag or ensign, as the white stars on a blue field in the flag of the U.S.
4. a building used for social recreation on a college or university campus
   in full student union
5. a device for joining together parts, as of a machine; esp., a coupling for linking the ends of pipes
6. a fabric made of two or more different kinds of material, as cotton and linen
7. Math. the set containing all the elements of two or more given sets, and no other elements

Etymology: ME < MFr < LL(Ec) unio < L, oneness, unity < unus, one