Geoff sent me this article and I just couldn't help wondering if this is where the slang word "dick" (meaning "penis") came from. The etymology dictionary says that the meaning of "penis" probably came from the 1891 Farmer's slang dictionary, but that's not really explaining the etymology. Any other ideas (besides mine) on how "dick" came to mean "penis?"

It only says it was attested in that dictionary. As the entry says, it came to mean "fellow, lad, man" from the 1550s. Thus, by transference, "manly part".

That's certainly possible - though lots of words are related to men that don't mean "penis."