From etymonline.com: ampersand. (n) 1837, contraction of and per se and, meaning '&' by itself is 'and' (a hybrid phrase, partly in Latin, partly in English).

From etymonline.com: ampersand. (n) 1837, contraction of and per se and, meaning '&' by itself is 'and' (a hybrid phrase, partly in Latin, partly in English). An earlier form of it was colloquial ampassy (1706). The distinction is to avoid confusion with "&" in such formations as "&c.", a once common way of writing "etc." (the et in et cetera is Latin for "and"). The letters a, I, and o also formerly (15c.-16c.) were written a per se, etc., especially when standing alone as words. The symbol is based on the Latin word et "and," and comes from an old Roman system of shorthand signs (ligatures) attested in Pompeiian graffiti... In old schoolbooks the ampersand was printed at the end of the alphabet and thus by 1880s the word ampersand had acquired a slang sense of "posterior, rear end, hindquarters." https://www.etymonline.com/word/ampersand https://www.etymonline.com/word/ampersand