In common parlance 2019 ‘reactionary’ has variously tight or loose definitions, along with the term ‘neoreactionary’, as does the term ‘leftism’. Historically both terms derive from around the French Revolution, and were then typically seen as antonyms.
Already in early 20th century Leftism, leftists were accusing each other of being leftist. Stalin is typically seen as having turned Bolshevism or the USSR to a more reactionary position, versus the more progressive aspects of other Marxist thought. Since National-Socialism is largely enough derived from Leftist thought, but mixes it with reactionary thought, some have referred to it as reactionary leftism. Nick Land would refer to reactionary leftism as pragmatic vs overly utopian socialism.
Can be stuff like Christian anarchism, since anarchism is typically regarded as Leftist but Christianity is reactionary by today's Lefto-Neoliberal Complex / Cathedral standards (i.e. Christianity is explicitly against pornea / infidelity per the NT). Tolstoy e.g. is a Christian anarchist — arguably the NT is anarcho-communist but obviously not totally antinomian or nihilist