Meaning of “union” - Learner’s Dictionary

union

noun uk us /ˈjuːnjən/
JOBS [ C ] (also UK trade union, also US labor union)
GROUP [ U, no plural ]

B2 a situation in which two or more countries, groups, etc join together to make one country, group, etc:

a move towards full economic union of EU countries
→ See also the European Union

(Definition of “union” from the Cambridge Learner’s Dictionary © Cambridge University Press)