Emily Dickinson Lexicon

SACK, n.³ [L. sagum, whence Gr. σαγος. But the word is Celtic or Teutonic; W. segan, a covering, a cloke.]

Among our rude ancestors, a kind of cloke of a square form, worn over the shoulders and body, and fastened in front by a clasp or thorn. It was originally made of skin, afterward of wool. In modern times, this name has been given to a woman's garment, a gown with loose plaits on the back; but no garment of this kind is now worn, and the word is in disuse. [See Varro, Strabo, Cluver, Bochart.]