The support of advocacy of a union, especially of a trade union. / (often capitalised) Support for the North (the Union) during the American Civil War.

To combine sets using the union operation.

(countable) The act of uniting or joining two or more things into one. / (countable) The state of being united or joined; a state of unity or harmony.

Belonging to, represented by, or otherwise pertaining to a labour union.

The 0-10-2 locomotive wheel arrangement.

(US, with determiner, dated, especially 19th century) The United States of America.

A surname.

(Oxford University, informal) The Oxford Union (a debating society); not to be conflated with Oxford University Student Union (a students' union).

plural of unionism

present participle of union