What does "unionism" mean?

The support of advocacy of a union, especially of a trade union.

Unionism

Common synonyms include: trade unionism, federation concept, integrationism, labor movement, political unification, unificationism.

noun

noun ·4 syllables ·Rare ·Advanced level

Noun

1
The support of advocacy of a union, especially of a trade union. countable, uncountable
"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."
2
the system or principles and theory of labor unions wordnet
3
Support for the North (the Union) during the American Civil War. capitalized, countable, often, uncountable
4
Support for the continuance of the United Kingdom (especially with respect to Northern Ireland). capitalized, countable, often, uncountable

"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."

From union + -ism.