[1] : The Collaborative International Dictionary of English v.0.48

cassia \cas"sia\ ka^sh".a, n. l. cassia and casia, gr.
   kassi`a and kasi`a; of semitic origin; cf. heb.
   qetsimac=ah, fr. q=atsa' to cut off, to peel off.
   1. bot. a genus of leguminous plants herbs, shrubs, or
      trees of many species, most of which have purgative
      qualities. the leaves of several species furnish the senna
      used in medicine.
      1913 webster

   2. the bark of several species of cinnamomum grown in
      china, etc.; chinese cinnamon. it is imported as cassia,
      but commonly sold as cinnamon, from which it differs more
      or less in strength and flavor, and the amount of outer
      bark attached.
      1913 webster

   note: the medicinal "cassia" cassia pulp is the laxative
         pulp of the pods of a leguminous tree cassia fistula
         or pudding-pipe tree, native in the east indies but
         naturalized in various tropical countries.
         1913 webster

   cassia bark, the bark of cinnamomum cassia, etc. the
      coarser kinds are called cassia lignea, and are often
      used to adulterate true cinnamon.

   cassia buds, the dried flower buds of several species of
      cinnamon cinnamomum cassia, atc...

   cassia oil, oil extracted from cassia bark and cassia buds;
      -- called also oil of cinnamon.
      1913 webster
see also:
cinnamomum cassia cassia fistula cassia bark cinnamomum cassia cassia lignea 
cassia buds cassia oil oil of cinnamon 

[2] : WordNet (r) 2.0

cinnamomum cassia
     n : chinese tree with aromatic bark; yields a less desirable
         cinnamon than ceylon cinnamon syn: cassia, cassia-bark
         tree
see also:
cassia cassia-bark tree 

Cinnamomum >> C Words
Cinnamomum, definition of term: Cinnamomum
cinnamomum_pag1.html

Cassia >> C Words
Cassia, definition of term: Cassia
cassia_pag1.html