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).
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   2. The catkin or strobilaceous fruit of the hop, much used in
      brewing to give a bitter taste.
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   3. The fruit of the dog-rose. See Hip.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Back \Back\, n. [F. bac: cf. Arm. bag, bak a bark, D. bak tray,
   bowl.]
   1. A large shallow vat; a cistern, tub, or trough, used by
      brewers, distillers, dyers, picklers, gluemakers, and
      others, for mixing or cooling wort, holding water, hot
      glue, etc.
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   Hop back, Jack back, the cistern which receives the
      infusion of malt and hops from the copper.

   Wash back, a vat in which distillers ferment the wort to
      form wash.

   Water back, a cistern to hold a supply of water; esp. a
      small cistern at the back of a stove, or a group of pipes
      set in the fire box of a stove or furnace, through which
      water circulates and is heated.
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   2. A ferryboat. See Bac, 1.
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