The Collaborative International Dictionary of English v.0.48:

Cinnamon \Cin"na*mon\, n. [Heb. qinn[=a]m[=o]n; cf. Gr. ?, ?,
   cinnamomum, cinnamon. The Heb. word itself seems to have been
   borrowed from some other language; cf. Malay k[=a]j[=u]
   m[=a]nis sweet wood.]
   (a) The inner bark of the shoots of Cinnamomum Zeylanicum,
       a tree growing in Ceylon. It is aromatic, of a moderately
       pungent taste, and is one of the best cordial,
       carminative, and restorative spices.
   (b) Cassia.
       [1913 Webster]

   Cinnamon stone (Min.), a variety of garnet, of a cinnamon
      or hyacinth red color, sometimes used in jewelry.

   Oil of cinnamon, a colorless aromatic oil obtained from
      cinnamon and cassia, and consisting essentially of
      cinnamic aldehyde, C6H5.C2H2.CHO.

   Wild cinnamon. See Canella.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cinnamon
    n 1: aromatic bark used as a spice [syn: cinnamon, cinnamon
         bark]
    2: tropical Asian tree with aromatic yellowish-brown bark;
       source of the spice cinnamon [syn: cinnamon, Ceylon
       cinnamon, Ceylon cinnamon tree, Cinnamomum zeylanicum]
    3: spice from the dried aromatic bark of the Ceylon cinnamon
       tree; used as rolled strips or ground