1That supports or advocates social democracy; specifically designating any of various political parties or movements that support or advocate social democracy; of or relating to these.
2Of a nation, state, etc.: governed or organized in accordance with the principles of social democracy.
3Of, relating to, or characteristic of social democracy or social democrats; characterized by (support for) social democracy or social democrats.
Mid 19th century; earliest use found in The Glasgow Herald. From social + democratic, probably after social democrat.