Douglas Harper's Etymology Dictionary
1925, also niggah, representing southern U.S. pronunciation of nigger (q.v.).
Wiktionary
n. (context ethnic slur vulgar slang often considered offensive but sometimes used affectionately especially in African American Vernacular English English) nigger.
WordNet
Wikipedia
Nigga (, pronounced identically to nigger in some dialects (including where common speech is non-rhotic; in rhotic dialects the latter is pronounced ) is a colloquial term used in Black English Vernacular that began as an eye dialect form of the word nigger (a word originated as a term used in a neutral context to refer to black people, as a variation of the Spanish/ Portuguese noun negro, a descendant of the Latin adjective niger, meaning the color " black").
Usage examples of "nigga".
And as my body grew into young manhood, lean-muscled, hard, slim and cool and handsome as any hip-hop nigga sucking magic money from the musical mammary, as I grew bigger and wiser and stronger with each passing day and year, my heart cold and smoking like dry ice, as the factory pumped out hard young muhfukkahs, cold and perfect as snowflakes-some graduating to the streets where they lived like kings or died like flies, some shipped off to adult institutions-and as the younger boys took their place in the food chain, I gained power, I took control.
And nigga, right about now I think I could use a prescription for Valium.
And that bad championship nigga got the last laugh, he laughing all the way to the bank.
And as my body grew into young manhood, lean-muscled, hard, slim and cool and handsome as any hip-hop nigga sucking magic money from the musical mammary, as I grew bigger and wiser and stronger with each passing day and year, my heart cold and smoking like dry ice, as the factory pumped out hard young muhfukkahs, cold and perfect as snowflakessome graduating to the streets where they lived like kings or died like flies, some shipped off to adult institutionsand as the younger boys took their place in the food chain, I gained power, I took control.
This ain't about niggas doin each other over a bunch of concrete nobody owns.