Yeah, that's why I nailed down the number for you with my next post.
"Uncle!" is another way of saying, "Okay, Uncle!" or "He cried Uncle!" ~ they are all variations for saying, "Okay, I give ~ You win." "I give" means "I give in. I stop disputing what you're saying or doing." As a child, when wrestling with someone, we would try to pin the other one down, on their back with shoulders to the ground, in order to 'win' ~ the one who was about to become victor would say, "Say Uncle! Say Uncle!" and the loser would ultimately have to give in and say, "Okay, Uncle!" Then, it was okay for the victor to release the loser, and the loser to get up off the floor/ground/wherever. It would be used in various other contexts of physical prowess [or unfairness

] ~ arm wrestling; pulling a person's arm up and behind their own back; or whatever. It is also applicable to verbal bantering, as I used it about whether that attempt to make a non-word was actually a word or not.
~ Lizzy