From Wikipedia: Mondegreen is the mishearing or misinterpretation of a phrase as a result of near-homophony.
As a child, my hearing was good, but sometimes the cognitive processes couldn't quite make sense of what I heard. Around Christmas time, as Silent Night was sung, I visualized "sleep in heavenly peace" as "sleep in heavenly peas."
Life goes on, I eventually learned the less interesting truth and put such things behind me.
Now, some 70+ years later, I am kidding Susan. She has a princess quality, and is truly sensitive to slight imperfections, particularly those that affect her comfort. Remember the pea under the mattress story? Anyhow, I try to accommodate her when I can, as she is genuinely distressed and can easily be made happy. I do, however, tease her a little about this princess quality. This morning as I proceeded to satisfy some request, I responded "yes, your highless".
Susan says "what did you say?"
Me "your highless."
Susan "it's highness."
Me, "no, I'll even show you in the dictionary." ... to the dictionary ...
"Curses, she is right!"
Later, I google to make sure, still disbelieving that I could get it wrong all these years. I graduated from college, even have an advanced degree, enjoy reading, and have encountered the term many times, still in my brain, it came through as highless. I think this qualifies as a one word mondegreen.