Medium reports: [edited]
The symbol “&” is an amalgam of the letters 'et', Latin for 'and'. The character is known as an ampersand.
It began with American children learning their ABCs. In the 1830s the alphabet started incorporating the symbol '&' as the 27th letter. Reciting the end of the alphabet would be confusing if it were 'X, Y, Z, and'.
So a couple of words of Latin were incorporated into the chant, 'X, Y, Z, and per se and'.
'Per se' is Latin for 'by itself'. Through routine repetition the phrase 'and per se and' transmogrified into 'ampersand'.
And it stuck.