Originally posted by Turnbull:
The Chin got his name because his first name is pronounced, in Italian, as Vin-CHEN-zo.
Depends on who you listen to. I've seen stories stating the moniker comes from his prominent chin (and this theory makes most sense to me - wiseguys love to make reference to physical traits), and also stories alluding to the fact his nickname came from his boxing career (ie. he had a weak chin and was knocked out a lot - this is less likely because he had a decent boxing record).
