2. A slow-witted person.
Nimrod was the Biblical founder of Babylon, also considered a mighty hunter. Contrary to the uneducated twits on here, Nimrod did NOT build the tower of Babel (at least the Bible does not claim this, only that the "men of Babylon" tried to build it), and the Bible does NOT claim he tried to kill God.
The Bible ONLY mentions that Nimrod was a son of Cush, the founder of Babylon, and a mighty hunter. Curiously enough, Dictionary.com attests definition 2 to have derived from a Looney Toons episode, wherein Bugs Bunny mocks his adversary, the hunter Elmer Fudd, calling him a "poor little Nimrod". Warner Brothers' Looney Toons cartoons were not written for children, but for literate adults, and often contained literary references children would not understand. Younger generations, mostly illiterate, and having little or no Bible knowledge not gleaned from their moronic parents and half-wit talk radio hosts, probably misunderstood the comment as being a general insult describing the slow-witted Fudd.