Green’s Dictionary of Slang

1. to present a (rock) concert; thus MC-ing/emceeing n.

1938		Ottowa Citizen (Ontario) 11 June 19/1: Douglas was picked to ‘emcee’ Phil’s swing show.
1938		Pittsburgh Courier (PA) 21 May 11/1: Billy Maples [...] did a bit of emceein’ on the side.
1940		J.H. O’Hara Pal Joey 4: I m.c.’d, and they had a couple of kids [...] doing tap.
1943		Pittsburgh Courier (PA) 22 May 21/1: He is emceeing a show that includes [etc].
1953		L. Durst Jives of Dr. Hepcat (1989) 6: We stop by a spot where it’s floor show time and a real gone guy is doing the emceeing and he has several artist male and female piano duet singers, dancers, etc., and it’s his job to keep the show moving and on time.
1959		C. MacInnes Absolute Beginners 136: A ballad-and-blues festival he was MC-ing [...] up there on Denmark Hill.
1965		L. Bruce How to Talk Dirty 28: The owner asked my mother to m.c.

2. to perform as a rapper.

2000		W. Shaw Westsiders 50: With a small number of exceptions, MC-ing has remained a boy thing.
2008		‘Grandmaster Flash’ Adventures 102: [T[his new DJ culture [...] was giving birth to a new form of expression that everything to do with talking shit. And the cats who were doing it called it MCing, which then became rap.
2017		Observer (London) New Rev. 19 Feb. 9/3: He’d actually been MCing (‘spitting bars’) since he was around 11.