Option #3 is deemed unlikely due to being too recent. Option #2 links to but the linkage or first use in poker usage is unclear.
It says #1 below is a common and certainlyapocryphal folk etymology. The main contenders are below (according to Wikipedia). Wikipedia gives the same possibilities as the referenced article, but the true origin is remarkably unclear. It means the best possible hand and though a well known term, no-one seems to know its origin. I read a interesting article regarding origin of the term “The Nuts” in Poker.
