Source : Webster's Revised Unabridged Dictionary (1913)

Ironwood \I"ron*wood`\, n. (Bot.)
   A tree unusually hard, strong, or heavy wood.

   Note: In the United States, the hornbeam and the hop hornbeam
         are so called; also the {Olneya Tesota}, a small tree
         of Arizona; in the West Indies, the {Erythroxylon
         areolatum}, and several other unrelated trees; in
         China, the {Metrosideros vera}; in India, the {Mesua
         ferrea}, and two species of {Inga}; in Australia, the
         {Eucalyptus Sideroxylon}, and in many countries,
         species of {Sideroxylon} and {Diospyros}, and many
         other trees.

Source : WordNet®

ironwood
     n 1: handsome East Indian evergreen tree often planted as an
          ornamental for its fragrant white flowers that yield a
          perfume; source of very heavy hardwood used for railroad
          ties [syn: {rose chestnut}, {ironwood tree}, {Mesua
          ferrea}]
     2: exceptionally tough or hard wood of any of a number of
        ironwood trees
     3: a small slow-growing deciduous tree of northern Iran having
        a low domed shape [syn: {iron tree}, {iron-tree}, {ironwood
        tree}]
     4: medium-sized hop hornbeam of eastern North America [syn: {Eastern
        hop hornbeam}, {ironwood tree}, {Ostrya virginiana}]