The Collaborative International Dictionary of English v.0.48:

Girder \Gird"er\, n. [From Gird to encircle.]
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   1. One who, or that which, girds.
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   2. (Arch. & Engin.) A main beam; a stright, horizontal beam
      to span an opening or carry weight, such as ends of floor
      beams, etc.; hence, a framed or built-up member
      discharging the same office, technically called a compound
      girder. See Illusts. of Frame, and Doubleframed floor,
      under Double.
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   Bowstring girder, Box girder, etc. See under Bowstring,
      Box, etc.

   Girder bridge. See under Bridge.

   Lattice girder, a girder consisting of longitudinal bars
      united by diagonal crossing bars.

   Half-lattice girder, a girder consisting of horizontal
      upper and lower bars connected by a series of diagonal
      bars sloping alternately in opposite directions so as to
      divide the space between the bars into a series of
      triangles. --Knight.

   Sandwich girder, a girder consisting of two parallel wooden
      beams, between which is an iron plate, the whole clamped
      together by iron bolts.
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The Collaborative International Dictionary of English v.0.48:

Box \Box\, n.; pl. Boxes [As. box a small case or vessel with
   a cover; akin to OHG. buhsa box, G. b["u]chse; fr. L. buxus
   boxwood, anything made of boxwood. See Pyx, and cf. Box a
   tree, Bushel.]
   1. A receptacle or case of any firm material and of various
      shapes.
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   2. The quantity that a box contain.
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   3. A space with a few seats partitioned off in a theater, or
      other place of public amusement.
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            Laughed at by the pit, box, galleries, nay, stage.
                                                  --Dorset.
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            The boxes and the pit are sovereign judges.
                                                  --Dryden.
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   4. A chest or any receptacle for the deposit of money; as, a
      poor box; a contribution box.
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            Yet since his neighbors give, the churl unlocks,
            Damning the poor, his tripple-bolted box. --J.
                                                  Warton.
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   5. A small country house. "A shooting box." --Wilson.
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            Tight boxes neatly sashed.            --Cowper.
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   6. A boxlike shed for shelter; as, a sentry box.
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   7. (Mach)
      (a) An axle box, journal box, journal bearing, or bushing.
      (b) A chamber or section of tube in which a valve works;
          the bucket of a lifting pump.
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   8. The driver's seat on a carriage or coach.
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   9. A present in a box; a present; esp. a Christmas box or
      gift. "A Christmas box." --Dickens.
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   10. (Baseball) The square in which the pitcher stands.
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   11. (Zool.) A Mediterranean food fish; the bogue.
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   Note: Box is much used adjectively or in composition; as box
         lid, box maker, box circle, etc.; also with modifying
         substantives; as money box, letter box, bandbox, hatbox
         or hat box, snuff box or snuffbox.
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   Box beam (Arch.), a beam made of metal plates so as to have
      the form of a long box.

   Box car (Railroads), a freight car covered with a roof and
      inclosed on the sides to protect its contents.

   Box chronometer, a ship's chronometer, mounted in gimbals,
      to preserve its proper position.

   Box coat, a thick overcoat for driving; sometimes with a
      heavy cape to carry off the rain.

   Box coupling, a metal collar uniting the ends of shafts or
      other parts in machinery.

   Box crab (Zool.), a crab of the genus Calappa, which,
      when at rest with the legs retracted, resembles a box.

   Box drain (Arch.), a drain constructed with upright sides,
      and with flat top and bottom.

   Box girder (Arch.), a box beam.

   Box groove (Metal Working), a closed groove between two
      rolls, formed by a collar on one roll fitting between
      collars on another. --R. W. Raymond.

   Box metal, an alloy of copper and tin, or of zinc, lead,
      and antimony, for the bearings of journals, etc.

   Box plait, a plait that doubles both to the right and the
      left.

   Box turtle or

   Box tortoise (Zool.), a land tortoise or turtle of the
      genera Cistudo and Emys; -- so named because it can
      withdraw entirely within its shell, which can be closed by
      hinged joints in the lower shell. Also, humorously, an
      exceedingly reticent person. --Emerson.

   In a box, in a perplexity or an embarrassing position; in
      difficulty. (Colloq.)

   In the wrong box, out of one's place; out of one's element;
      awkwardly situated. (Colloq.) --Ridley (1554)
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WordNet (r) 3.0 (2006):

box girder
    n 1: a beam built up from boards; has a hollow rectangular cross
         section [syn: box beam, box girder]