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]

WordNet (r) 3.0 (2006):

Sontag
    n 1: United States writer (born in 1933) [syn: Sontag, Susan
         Sontag]