Ampersand \AM-per-sand\ or \am-per-SAND\ , noun;
1. A character or symbol for "and"
This word is a mondegreen* that dates to the early 1800's. For more, check out Dictionary.com's article.
*A mondegreen is a misinterpretation of a word or phrase that sounds like another word or phrase that has been heard. For a humorous dose of mondegreens, check out KissThisGuy.com