There was a time when the small character “&” was regarded as the 27th part of the alphabet. In the first century, Roman scribes wrote in cursive, so when they wrote the Latin word et, which means “and”, they linked the e and t. Gradually, the combined letters e and t came together to signify the word “and” in English as well.
In the early 1800s, school children reciting their ABCs used to conclude the alphabet with the “&”. However, it would have been confusing to say “X, Y, Z, AND.”
Instead, the students used to say, “and per se and.” Here “Per se” means “by itself,” So the students were essentially saying, “X, Y, Z, and by itself and.”
Over time, “and per se and” was slurred together into the word we use today – ampersand. Today, whenever a word comes about from a mistaken pronunciation, it is called a “Mondegreen.”