This is so interesting - from Wikepedia, the ampersand can be traced back to the 1st century A.D. and the Old Roman cursive, in which the letters E and T occasionally were written together to form a ligature. Traditionally, in English-speaking schools when reciting the alphabet, any letter that could also be used as a word in itself ("A", "I", and, at one point, "O") was preceded by the Latin expression per se (Latin for "by itself"). Also, it was common practice to add at the end of the alphabet the "&" sign as the 27th letter, pronounced and. Thus, the recitation of the alphabet would end in: "X, Y, Z and per se and". This last phrase was routinely slurred to "ampersand" and the term crept into common English usage by around 1837.