"Little Joe" = four?!?!

This question spawns from the “junion/senior” question also on this forum. In it, as an aside, I asked what a suitable nickname for a IV would be (i.e. Senior, Junior, Trey, ____ ).

Well, I’m at work, and I decided to consult the first source at hand–Corel WP8’s Thesaurus. It offers “Little Joe” as a synonym for “four.”

What the hell is going on here? Does this mean that the number two inheritor of a name can be called “Hoss,” also like in Bonanza? Or is there a more valid explanation for this term?

(And yes, I know I should consult a more comprehensive source. But I’m at work, remember?)

Is “Little Joe” slang for four from Craps?
Like “Snake Eyes” or “Boxcars”?