The Collaborative International Dictionary of English v.0.48:

Sontag \Son"tag\, n. [So called from from Mme. Henriette Sontag,
   a famous singer.]
   A knitted worsted jacket, worn over the waist of a woman's
   dress.
   [1913 Webster]

U.S. Gazetteer (1990):

Sontag, MS
  Zip code(s): 39665