The Collaborative International Dictionary of English v.0.48:

Rood \Rood\ (r[=oo]d), n. [AS. r[=o]d a cross; akin to OS.
   r[=o]da, D. roede rod, G. ruthe, rute, OHG. ruota. Cf. Rod
   a measure.]
   1. A representation in sculpture or in painting of the cross
      with Christ hanging on it.
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   Note: Generally, the Trinity is represented, the Father as an
         elderly man fully clothed, with a nimbus around his
         head, and holding the cross on which the Son is
         represented as crucified, the Holy Spirit descending in
         the form of a dove near the Son's head. Figures of the
         Virgin Mary and of St. John are often placed near the
         principal figures.
         [1913 Webster]

               Savior, in thine image seen
               Bleeding on that precious rood.    --Wordsworth.
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   2. A measure of five and a half yards in length; a rod; a
      perch; a pole. [Prov. Eng.]
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   3. The fourth part of an acre, or forty square rods.
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   By the rood, by the cross; -- a phrase formerly used in
      swearing. "No, by the rood, not so." --Shak.

   Rood beam (Arch.), a beam across the chancel of a church,
      supporting the rood.

   Rood loft (Arch.), a loft or gallery, in a church, on which
      the rood and its appendages were set up to view. --Gwilt.

   Rood screen (Arch.), a screen, between the choir and the
      body of the church, over which the rood was placed.
      --Fairholt.

   Rood tower (Arch.), a tower at the intersection of the nave
      and transept of a church; -- when crowned with a spire it
      was called also rood steeple. --Weale.

   Rood tree, the cross. [Obs.] "Died upon the rood tree."
      --Gower.
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WordNet (r) 3.0 (2006):

rood screen
    n 1: a screen in a church; separates the nave from the choir or
         chancel