Reactionary is a word which describes the politics of the far right. It’s a reaction against social progress or against the movements pushing for social progress. Fascism is a reaction against socialism and communism, it’s the current ruling class (these days, the bourgeoisie, but also in the past the aristocracy and monarchs) reacting with violence and repression against the social movements that want to overthrow them or put limits on their power and take power for the working class.