Our youngest made up a lot of words. When she was a baby, she was a "head banger." This banging was usually aimed at people's heads. It hurt, big hard fat baby head! We used to say, "No banging!" and she'd yell, "BYNA BYNA BYNA BYNA!" I imagine she was trying to say "Banging." She learned that if she banged her head on certain stuff, like say, concrete, it would hurt. So, "Byna" became her word for "owie" or hurt.
When she was in Nursery School she had said something about "getting a Byna" and I asked her, "I like the word Byna. Is 'Byna' a real word, or did you make it up?"
HER: "It a real word."
ME: "OK. So do your friends at school use it, too?"
She waved her little hand in my face and said, "I don't wanna talk about it!" Her tone was so adult, it was hilarious.
When she was a toddler, her teenage sisters would go out in the evening, she would say, "Bye Bye, have a good time. Don't get a Byna!" I guess she was initiating my dh and I saying, "Be careful."
She's 14 now, and she and our entire family still uses the word.