Not ionic.

(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.

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 union

Third-person singular simple present indicative form of union