ampersand (n.) Look up ampersand at Dictionary.com
1837, contraction of and per se and, meaning "(the character) '&' by itself is 'and' " (a hybrid phrase, partly in Latin, partly in English). The distinction is to avoid confusion of & in such formations as &c., a once common way of writing etc. (remembering that the et in it 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 a word.

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, but not (as sometimes stated) from the Tironian Notes, which was a different form of shorthand, probably invented by Cicero's companion Marcus Tullius Tiro, which used a different symbol, something like a reversed capital gamma, to indicate et.

This Tironian symbol was maintained by some medieval scribes, including Anglo-Saxon chroniclers, who sprinkled their works with a symbol like a numeral 7 to indicate the word and. In old schoolbooks the ampersand was printed at the end of the alphabet and thus by 1880s had acquired a slang sense of "posterior, rear end, hindquarters."