capo dei capi: "boss of all [the] bosses" is a phrase used mainly by the media, public and the law enforcement community to indicate a supremely powerful crime boss in the Sicilian or American Mafia who holds great influence over the whole organization.
captain: a capo.
cement shoes: a method of murder or body disposal, usually associated with criminals such as the Mafia or gangs. It involves weighting down the victim, who may be dead or alive, with concrete and throwing them into water in the hope the body will never be found.
clip: to murder; also to whack, hit, pop, burn, ice, put a contract out on.
code of silence: not ratting on one's colleagues once one has been pinched -- no longer a strong virtue in organized crime families. Also, see omertà.
earner: a member who brings in a lot of money for the family
eat alone: to keep for oneself; to be greedy.
family: an organized crime clan, like the Genoveses, the Gambinos, or the Sopranos.
forget about it (often pronounced "fuggedaboutit"): An exclamation; as the title character explains in Donnie Brasco:
"Forget about it" is, like, if you agree with someone, you know, like "Raquel Welch is one great piece of ass. Forget about it!" But then, if you disagree, like "A Lincoln is better than a Cadillac? Forget about it!" You know? But then, it's also like if something's the greatest thing in the world, like, "Minchia! Those peppers! Forget about it!" But it's also like saying "Go to hell!" too. Like, you know, like "Hey Paulie, you got a one inch pecker?" and Paulie says "Forget about it!" Sometimes it just means "Forget about it."
shakedown: to blackmail or try to get money from someone; also to give someone a scare.
shy: the interest charged on loans by loan sharks.
shylockbusiness: the business of loansharking.
soldier: the bottom-level member of an organized crime Family who is made, as in "foot soldiers."
spring cleaning: cleaning up, hiding or getting rid of evidence.
tax: to take a percentage of someone's earnings.
The Commission and the Sicilian Mafia Commission: two bodies, Italian-American and the Sicilian respectively, of leading Mafia members to decide on important questions concerning the actions of, and settling disputes within the Mafia.
This Thing of Ours (Cosa Nostra): a mob family, or the entire mob.
through the eye: a message job through the eye to say "We're watching you!"
through the mouth: a message job through the mouth to indicate that someone WAS a rat.