Definition of "unionism"

unionism

noun
countable and uncountable, plural unionisms
1. The support of advocacy of a union, especially of a trade union.
  Quotations
  This isn't the time for militant unionism. If I were at ScotRail, in the current climate I'd trade a pay freeze [sic: pay rise?] for job security.
  2020 December 2, Philip Haigh, “A winter of discontent caused by threat of union action”, in Rail, page 63
2. (often capitalised) Support for the North (the Union) during the American Civil War.
3. (often capitalised) Support for the continuance of the United Kingdom (especially with respect to Northern Ireland).