BIGpedia - Union - Encyclopedia and Dictionary Online

A Union is a single entity which is a collection of two or more entities.

Other references are:

A mathematical concept: see union (set theory)
A political entity of states: see personal union
The United States of America, particularly in reference to actions during the American Civil War (see Union (American Civil War))
The European Union
The African Union
A type of legal entity: see union (commerce)
A trade union (also known as a labor union or labour union) is a workers' organization designed to assist in employment negotiation.
A datatype; see union (computer science)
Civil union - a commitment ceremony similar to but legally distinct from marriage
The successful fusion of a fractured bone.
Union College - a college in Schenectady, New York and other places.
Union of India - was the official name of India before it became a republic.
Union Theological College - a college in Northern Ireland
The United States Republican Party was also known as the Union Party during the 1864 election cycle.