(countable) A union is when many things are joined together.
- Synonyms: alliance, association, confederation, corporation, federation, marriage and merger
- Antonyms: diaspora, dispersion and individual
The League of Nations was a union between many nations.
(countable) A union may be the act of joining.
- Synonyms: fusion, joining, marriage, merger and unification
- Antonyms: break, divorce and succession
The union of these two companies was painless.

Marriage is the union of two lives.

Noun