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That could be close to the actual etymology. I believe “Nimrod” is the name of a person in the Bible.
Nimrod is a biblical figure mentioned in the Book of Genesis and Books of Chronicles. The son of Cush and therefore a great-grandson of Noah, Nimrod was described as a king in the land of Shinar. The Bible states that he was “a mighty hunter before the Lord [and]… began to be mighty in the earth”.
Some funny trivia with “might hunter”: Bugs Bunny called Elmer Fudd nimrod, saying something like “nice shot, nimrod!” – the insult was that Elmer was a bad hunter. But the obscure reference was lost on most people, much less a child audience (myself included), and so nimrod became a generic insult akin to “idiot” or "imbecile.