gown (n.) Look up gown at Dictionary.com
c.1300, from Old French goune "robe, coat, habit, gown," from Late Latin gunna "leather garment, skin, hide," of unknown origin. Used by St. Boniface (8c.) for a fur garment permitted for old or infirm monks. Klein writes it is probably "a word adopted from a language of the Apennine or the Balkan Peninsula." OED points to Byzantine Greek gouna, a word for a coarse garment sometimes made of skins, but also notes "some scholars regard [Late Latin gunna] as of Celtic origin."

In 18c., gown was the common word for what is now usually styled a dress. It was maintained more in the U.S. than in Britain, but was somewhat revived 20c. in fashion senses and in comb. forms (such as bridal gown, nightgown). Meaning "flowing robe worn as a badge of office or authority" is from late 14c., on image of the Roman toga. As collective singular for "residents of a university" (1650s) it usually now is opposed to town.