Unionist

The word Unionist, simply meaning one espousing a union, has a number of connotations, depending on context:

Unionists are people in Ireland, England, Scotland and Wales who were historically in favour of uniting their nations into the United Kingdom, or who in modern times wish their the subsequent constituent parts to remain part of the United Kingdom.
For greater detail on Unionists in Ireland see the article Unionists (Ireland); for greater detail on Unionists in Scotland see Unionists (Scotland), Scottish Unionist Party and Conservative Party (UK) (the full name of which is the Conservative and Unionist Party).
Unionists are also people who support the political union between Romania and the Republic of Moldova
Members and supporters of trades unions also bear the label of unionists. See also syndicalism.
Unionist is also a term used to describe someone loyal to the Union Forces during the American Civil War. For greater detail on American Unionists see the article Union (American Civil War).
The Unionist Party (Canada) was a merger of parties that led Canada during World War I.