The Collaborative International Dictionary of English v.0.48:

Cascarilla \Cas`ca*ril"la\, n. [Sp., small thin bark, Peruvian
   bark, dim. of c['a]scara bark.] (Bot.)
   A euphorbiaceous West Indian shrub (Croton Eleutheria);
   also, its aromatic bark.
   [1913 Webster]

   Cascarilla bark (or Cascarilla) (Med.), the bark of
      Croton Eleutheria. It has an aromatic odor and a warm,
      spicy, bitter taste, and when burnt emits a musky odor. It
      is used as a gentle tonic, and sometimes, for the sake of
      its fragrance, mixed with smoking tobacco, when it is said
      to occasion vertigo and intoxication.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cascarilla
    n 1: West Indian shrub with aromatic bark [syn: cascarilla,
         Croton eluteria]