The Collaborative International Dictionary of English v.0.48:

Calumba \Ca*lum"ba\, n. [from kalumb, its native name in
   Mozambique.] (Med.)
   The root of a plant (Jateorrhiza Calumba, and probably
   Cocculus palmatus), indigenous in Mozambique. It has an
   unpleasantly bitter taste, and is used as a tonic and
   antiseptic. [Written also colombo, columbo, and
   calombo.]
   [1913 Webster]

   American calumba, the Frasera Carolinensis, also called
      American gentian. Its root has been used in medicine as
      bitter tonic in place of calumba.
      [1913 Webster]

WordNet (r) 3.0 (2006):

American gentian
    n 1: any of various tall perennial herbs constituting the genus
         Frasera; widely distributed in warm dry upland areas of
         California, Oregon, and Washington [syn: columbo,
         American columbo, deer's-ear, deer's-ears, pyramid
         plant, American gentian]