Definitions of union:

• noun:   the act of making or becoming a single unit

  Example: "The union of opposing factions"

• noun:   a device on a national flag emblematic of the union of two or more sovereignties (typically in the upper inner corner)
• noun:   the occurrence of a uniting of separate parts

  Example: "Lightning produced an unusual union of the metals"

• noun:   a set containing all and only the members of two or more given sets

  Example: "Let C be the union of the sets A and B"

• noun:   an organization of employees formed to bargain with the employer

  Example: "You have to join the union in order to get a job"

• noun:   a political unit formed from previously independent people or organizations

  Example: "The Soviet Union"

• noun:   the United States (especially the northern states during the American Civil War)

  Example: "He has visited every state in the Union"

• noun:   healing process involving the growing together of the edges of a wound or the growing together of broken bones
• noun:   the state of being joined or united or linked

  Example: "There is strength in union"

• noun:   the state of being a married couple voluntarily joined for life (or until divorce)

  Example: "God bless this union"

• noun:   the act of pairing a male and female for reproductive purposes
• adjective:   being of or having to do with the northern United States and those loyal to the Union during the Civil War

  Example: "Union soldiers"

• adjective:   of trade unions

  Example: "The union movement"

• name:  A surname (very rare: popularity rank in the U.S.: #36611)