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crony, close pal, buddy, trusted friend, adviser. Literally, "godfather" in Italian.
You can read about all the cold blooded goombata in Nicholas Pileggi's Wiseguy.

Christian and Anthony are my goombata.
by Jiggle Shopper May 28, 2012
An Italian American's mistress, but must be married ( the husband )
Tony's wife caught him with his goombata.
by jersey's goomba August 14, 2009