noun

• (countable) The act of uniting or joining two or more things into one.
• (uncountable) The state of being united or joined; a state of unity or harmony.
• (countable) Something united, or made one; something formed by a combination or coalition of parts or members; a confederation; a consolidated body; a league.
• (countable) A trade union; a workers' union.
  "In the autumn there was a row at some cement works about the unskilled labour men. A union had just been started for them and all but a few joined. One of these blacklegs was laid for by a picket and knocked out of time."

verb

• (set theory) To combine sets using the union operation.

adj

• (India) federal.
  "The union government of India"

name

• (US, with determiner, dated, especially 19th century) The United States of America.
  "threats to secede from the Union"
• (US, with determiner, historical) Those of the United States that did not secede at the time of the Civil War (of the United States of America).
  "Union troops at Gettysburg"
• (with determiner, historical) The Soviet Union: the proper noun Union is the standard English translation of the proper noun Союз (Sojuz), and All-Union is the standard English translation of всесоюзный (vsesojuznyj).
  "throughout the Union, but nowhere more so than at the Center [Moscow]"
• (chiefly India, with determiner, law) Alternative form of union.