It is a combination of two words:
Nigro which means black in latin.
And philia that means love or attraction.
Making it Black love which is love of black people/africans/afro-americans/jamaicans ETC...
Negrosity is a term used to describe how black someone or something is. Once someone's Negrosity Levels rise to a certain level they may often start to radiate Negrotism.
Johnny smoked a Jeffrey and his Negrosity levels instantly rose so high that he started to radiate Negrotism.