Source : Webster's Revised Unabridged Dictionary (1913)

Cascara sagrada \Cas"ca*ra sa*gra"da\ [Sp.]
   Holy bark; the bark of the California buckthorn ({Rhamnus
   Purshianus}), used as a mild cathartic or laxative.

Source : WordNet®

cascara sagrada
     n : dried bark of the cascara buckthorn used as a laxative [syn:
          {cascara}, {chittam bark}, {chittem bark}]