Jim Crow Look up Jim Crow at Dictionary.com
"black man," 1838, American English, originally the name of a black minstrel character in a popular song-and-dance act by T.D. Rice (1808-1860) that debuted 1828 and attained national popularity by 1832:
Wheel about, an' turn about, an' do jis so;
Eb'ry time I wheel about, I jump Jim Crow.
Where and how Rice got it, or wrote it, is a mystery. Even before that, crow (n.) had been a derogatory term for a black man. Association with segregation dates from 1842, in reference to a railroad car for blacks. Modern use as a type of racial discrimination is from 1943. In later 19c., Jim Crow also could be a reference to someone's change of (political) principles (1837, from the "jump" in the song) or reversible machinery (1875, "wheel about").