The Collaborative International Dictionary of English v.0.48:

Hornbeam \Horn"beam`\, n. [See Beam.] (Bot.)
   A tree of the genus Carpinus (Carpinus 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 Carpinus Betulus. The American is called also
   blue beech and water beech.
   [1913 Webster]

   Hop hornbeam. (Bot.) See under Hop.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hop \Hop\, n. [OE. hoppe; akin to D. hop, hoppe, OHG. hopfo, G.
   hopfen; cf. LL. hupa, W. hopez, Armor. houpez, and Icel.
   humall, SW. & Dan. humle.]
   1. (Bot.) A climbing plant (Humulus Lupulus), having a
      long, twining, annual stalk. It is cultivated for its
      fruit (hops).
      [1913 Webster]

   2. The catkin or strobilaceous fruit of the hop, much used in
      brewing to give a bitter taste.
      [1913 Webster]

   3. The fruit of the dog-rose. See Hip.
      [1913 Webster]

   Hop back. (Brewing) See under 1st Back.

   Hop clover (Bot.), a species of yellow clover having heads
      like hops in miniature (Trifolium agrarium, and
      Trifolium procumbens).

   Hop flea (Zool.), a small flea beetle (Haltica concinna),
      very injurious to hops.

   Hop fly (Zool.), an aphid (Phorodon humuli), very
      injurious to hop vines.

   Hop froth fly (Zool.), an hemipterous insect (Aphrophora
      interrupta), allied to the cockoo spits. It often does
      great damage to hop vines.

   Hop hornbeam (Bot.), an American tree of the genus Ostrya
      (Ostrya Virginica) the American ironwood; also, a
      European species (Ostrya vulgaris).

   Hop moth (Zool.), a moth (Hypena humuli), which in the
      larval state is very injurious to hop vines.

   Hop picker, one who picks hops.

   Hop pole, a pole used to support hop vines.

   Hop tree (Bot.), a small American tree (Ptelia
      trifoliata), having broad, flattened fruit in large
      clusters, sometimes used as a substitute for hops.

   Hop vine (Bot.), the climbing vine or stalk of the hop.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hop hornbeam
    n 1: any of several trees resembling hornbeams with fruiting
         clusters resembling hops