The Collaborative International Dictionary of English v.0.48:

Ptisan \Ptis"an\, n. [L. ptisana peeled barley, barley water,
   Gr. ?, from ? to peel, husk; cf. F. ptisane, tisane.]
   1. A decoction of barley with other ingredients; a
      farinaceous drink.
      [1913 Webster]

   2. (Med.) An aqueous medicine, containing little, if any,
      medicinal agent; a tea or tisane.
      [1913 Webster]