The Collaborative International Dictionary of English v.0.48:

Rue \Rue\ (r[udd]), n. [F. rue, L. ruta, akin to Gr. "ryth`; cf.
   AS. r[=u]de.]
   1. (Bot.) A perennial suffrutescent plant (Ruta
      graveolens), having a strong, heavy odor and a bitter
      taste; herb of grace. It is used in medicine.
      [1913 Webster]

            Then purged with euphrasy and rue
            The visual nerve, for he had much to see. --Milton.
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            They [the exorcists] are to try the devil by holy
            water, incense, sulphur, rue, which from thence, as
            we suppose, came to be called herb of grace. --Jer.
                                                  Taylor.
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   2. Fig.: Bitterness; disappointment; grief; regret.
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   Goat's rue. See under Goat.

   Rue anemone, a pretty springtime flower (Thalictrum
      anemonides) common in the United States.

   Wall rue, a little fern (Asplenium Ruta-muraria) common
      on walls in Europe.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wall \Wall\, n. [AS. weall, from L. vallum a wall, vallus a
   stake, pale, palisade; akin to Gr. ? a nail. Cf. Interval.]
   [1913 Webster]
   1. A work or structure of stone, brick, or other materials,
      raised to some height, and intended for defense or
      security, solid and permanent inclosing fence, as around a
      field, a park, a town, etc., also, one of the upright
      inclosing parts of a building or a room.
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            The plaster of the wall of the King's palace. --Dan.
                                                  v. 5.
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   2. A defense; a rampart; a means of protection; in the
      plural, fortifications, in general; works for defense.
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            The waters were a wall unto them on their right
            hand, and on their left.              --Ex. xiv. 22.
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            In such a night,
            Troilus, methinks, mounted the Troyan walls. --Shak.
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            To rush undaunted to defend the walls. --Dryden.
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   3. An inclosing part of a receptacle or vessel; as, the walls
      of a steam-engine cylinder.
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   4. (Mining)
      (a) The side of a level or drift.
      (b) The country rock bounding a vein laterally. --Raymond.
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   Note: Wall is often used adjectively, and also in the
         formation of compounds, usually of obvious
         signification; as in wall paper, or wall-paper; wall
         fruit, or wall-fruit; wallflower, etc.
         [1913 Webster]

   Blank wall, Blind wall, etc. See under Blank, Blind,
      etc.

   To drive to the wall, to bring to extremities; to push to
      extremes; to get the advantage of, or mastery over.

   To go to the wall, to be hard pressed or driven; to be the
      weaker party; to be pushed to extremes.

   To take the wall. to take the inner side of a walk, that
      is, the side next the wall; hence, to take the precedence.
      "I will take the wall of any man or maid of Montague's."
      --Shak.

   Wall barley (Bot.), a kind of grass (Hordeum murinum)
      much resembling barley; squirrel grass. See under
      Squirrel.

   Wall box. (Mach.) See Wall frame, below.

   Wall creeper (Zool.), a small bright-colored bird
      (Tichodroma muraria) native of Asia and Southern Europe.
      It climbs about over old walls and cliffs in search of
      insects and spiders. Its body is ash-gray above, the wing
      coverts are carmine-red, the primary quills are mostly red
      at the base and black distally, some of them with white
      spots, and the tail is blackish. Called also spider
      catcher.

   Wall cress (Bot.), a name given to several low cruciferous
      herbs, especially to the mouse-ear cress. See under
      Mouse-ear.

   Wall frame (Mach.), a frame set in a wall to receive a
      pillow block or bearing for a shaft passing through the
      wall; -- called also wall box.

   Wall fruit, fruit borne by trees trained against a wall.

   Wall gecko (Zool.), any one of several species of Old World
      geckos which live in or about buildings and run over the
      vertical surfaces of walls, to which they cling by means
      of suckers on the feet.

   Wall lizard (Zool.), a common European lizard (Lacerta
      muralis) which frequents houses, and lives in the chinks
      and crevices of walls; -- called also wall newt.

   Wall louse, a wood louse.

   Wall moss (Bot.), any species of moss growing on walls.

   Wall newt (Zool.), the wall lizard. --Shak.

   Wall paper, paper for covering the walls of rooms; paper
      hangings.

   Wall pellitory (Bot.), a European plant (Parictaria
      officinalis) growing on old walls, and formerly esteemed
      medicinal.

   Wall pennywort (Bot.), a plant (Cotyledon Umbilicus)
      having rounded fleshy leaves. It is found on walls in
      Western Europe.

   Wall pepper (Bot.), a low mosslike plant (Sedum acre)
      with small fleshy leaves having a pungent taste and
      bearing yellow flowers. It is common on walls and rocks in
      Europe, and is sometimes seen in America.

   Wall pie (Bot.), a kind of fern; wall rue.

   Wall piece, a gun planted on a wall. --H. L. Scott.

   Wall plate (Arch.), a piece of timber placed horizontally
      upon a wall, and supporting posts, joists, and the like.
      See Illust. of Roof.

   Wall rock, granular limestone used in building walls. [U.
      S.] --Bartlett.

   Wall rue (Bot.), a species of small fern (Asplenium
      Ruta-muraria) growing on walls, rocks, and the like.

   Wall spring, a spring of water issuing from stratified
      rocks.

   Wall tent, a tent with upright cloth sides corresponding to
      the walls of a house.

   Wall wasp (Zool.), a common European solitary wasp
      (Odynerus parietus) which makes its nest in the crevices
      of walls.
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WordNet (r) 3.0 (2006):

wall rue
    n 1: small delicate spleenwort found on a steep slope (as a wall
         or cliff) of Eurasia and North America [syn: wall rue,
         wall rue spleenwort, Asplenium ruta-muraria]