Green’s Dictionary of Slang

nigger adj.

also neger, niggah, nigra, nigrah
[nigger n.1 (1)]

1. [early 19C+] (orig. US) a derog. term indicating something or someone associated with black culture; thus as derog., contemptible, odd, inferior.

2. [mid-late 19C] prtaining to ‘nigger’ minstrels (usu. white singers in blackface).