MC

MC denotes Master of Ceremonies. The term for a lyricist who expresses himself in the vocal art of rap. For Rakim, MC means "move the crowd". In modern lingua franca, participants of hip-hop culture refer to the mc not just as the rapper, but the voice of their culture (as in, "Mos Def's conscious lyrics make us want to crown him MC reason.

I've heard that the prefix Mc- or Mac- in a person's name can be replaced by son of-. For example: McArthur can be understood as son of arthur. I think the intention was to say what clan you belonged to. So if you met Pidi from the clan of the Cloud, you could call him Pidi McCloud. The later use in family names is pretty natural from there.

ooh! just found a node mentioning that: Irish Gaelic family names

Update: gleeme says: a similiar prefix Fitz- (e.g. as in "Fitzpatrick") means bastard son of while Mc- means legitimate son of.