When it comes to the NY families, "lieutenant" was never an official rank within the Mafia. No boss called his underlings for lieutenants.
That's right, Hairy.
I think the term came about in the media, then later in Hollywood because it sounds dramatic, even theatrical. Frankly, it alway bugs me a bit when I read it.
The same thing with "Murder Inc". I doubt very much that the members of that gang called themselves "Murder Inc". In my opinion, "Murder Inc" was totally a media invention.
They referrered to themselves as the "Combination" or "National Combination". A ny reporter came up with "Murder Inc.". I think NYTimes came up with "syndicate".
