Robert was reminded of this today.
From the article about letters that didn’t make the alphabet here.
Today we just use it for stylistic purposes (and when we’ve run out of space in a text message or tweet), but the ampersand has had a long and storied history in English, and was actually frequently included as a 27th letter of the alphabet as recently as the 19th century.
In fact, it’s because of its placement in the alphabet that it gets its name. Originally, the character was simply called “and” or sometimes “et” (from the Latin word for and, which the ampersand is usually stylistically meant to resemble). However, when teaching children the alphabet, the & was often placed at the end, after Z, and recited as “and per se and,” meaning “and in and of itself” or “and standing on its own.”
So you’d have “w, x, y, z, and, per se, and.” Over time, the last bit morphed into “ampersand,” and it stuck even after we quit teaching it as part of the alphabet.