Pertaining to a union. / (rare, relational) Pertaining to the European Union.

Not ionic.

To combine sets using the union operation.

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

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.