Definition of: Social Democrat

1. A member of the Social Democratic party of Germany, founded by Bebel and Liebknecht in 1869 and based on Marxian principles. In 1875 it was merged with Lassalle's General German Workmen's Association. Under the Republic (1918–33) it advocated the principles embedded in the Weimar Constitution.
2. A member of a similar party in other countries.
—so′cial–dem′o·crat′ic adjective