1 [count] : an organization of workers formed to protect the rights and interests of its members ▪ She joined the teachers' union. ▪ union members/leaders/officials —called also (US) labor union (Brit) trade union
2 [noncount] : an act of joining two or more things together ▪ An embryo is created through the union of sperm and egg. ▪ a perfect union of Eastern and Western music
3 [singular] : a group of states or nations that are ruled by one government or that agree to work together ▪ the former Soviet Union ▪ the European Union
4 the Union a : the United States ▪ Utah joined the Union in 1896. ◊The State of the Union address is a yearly speech given by the U.S. President to Congress and the people to tell them about important things that are affecting the country. b : the group of northern states that supported the federal government during the American Civil War ▪ One brother fought for the Union and one for the Confederacy. —often used as Union before another noun ▪ Union soldiers
5 [count] : an organized group of people, businesses, etc., that have the same purpose or interest ▪ the American Civil Liberties Union ▪ the International Skating Union —see also student union
6 formal : the act of getting married or of causing two people to be married [noncount] ▪ the union of two people in marriage [count] ▪ They celebrated their union [=marriage] with more than 200 friends and family members. —see also civil union
7 [count, noncount] formal : the activity or an act of having sex ▪ sexual union