Source : Webster's Revised Unabridged Dictionary (1913)

Hornbeam \Horn"beam`\, n. [See {Beam}.] (Bot.)
   A tree of the genus {Carpinus} ({C. Americana}), having a
   smooth gray bark and a ridged trunk, the wood being white and
   very hard. It is common along the banks of streams in the
   United States, and is also called {ironwood}. The English
   hornbeam is {C. Betulus}. The American is called also {blue
   beech} and {water beech}.

   {Hop hornbeam}. (Bot.) See under {Hop}.

Source : WordNet®

hornbeam
     n : any of several trees or shrubs of the genus Carpinus