Etymology: Middle English, from Anglo-French, from Late Latin union-, unio oneness, union, from Latin unus one — more at one
Date: 15th century
a. an act or instance of uniting or joining two or more things into one: as
(1) the formation of a single political unit from two or more separate and independent units
(2) a uniting in marriage; also sexual intercourse
(3) the growing together of severed parts
b. a unified condition ; combination, junction <a gracious union of excellence and strength> 2. something that is made one ; something formed by a combining or coalition of parts or members: as a. a confederation of independent individuals (as nations or persons) for some common purpose b. (1) a political unit constituting an organic whole formed usually from units which were previously governed separately (as England and Scotland in 1707) and which have surrendered or delegated their principal powers to the government of the whole or to a newly created government (as the United States in 1789) (2) capitalized the federal union of states during the period of the American Civil War c. capitalized an organization on a college or university campus providing recreational, social, cultural, and sometimes dining facilities; also the building housing such an organization d. the set of all elements belonging to one or more of a given collection of two or more sets — called also join, sum e. labor union 3. a. a device emblematic of the union of two or more sovereignties borne on a national flag typically in the upper inner corner or constituting the whole design of the flag b. the upper inner corner of a flag 4. any of various devices for connecting parts (as of a machine); especially a coupling for pipes or pipes and fittings II. adjective Date: 1707 of, relating to, dealing with, or constituting a union; especially capitalized of, relating to, or being the side favoring the Union in the American Civil War <Union troops>
New Collegiate Dictionary. 2001.