The Collaborative International Dictionary of English v.0.48:

Prune \Prune\, v. t. [imp. & p. p. Pruned; p. pr. & vb. n.
   Pruning.] [OE. proine, probably fr. F. provigner to lay
   down vine stocks for propagation; hence, probably, the
   meaning, to cut away superfluous shoots. See Provine.]
   1. To lop or cut off the superfluous parts, branches, or
      shoots of; to clear of useless material; to shape or
      smooth by trimming; to trim: as, to prune trees; to prune
      an essay. --Thackeray.
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            Taking into consideration how they [laws] are to be
            pruned and reformed.                  --Bacon.
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            Our delightful task
            To prune these growing plants, and tend these
            flowers.                              --Milton.
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   2. To cut off or cut out, as useless parts.
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            Horace will our superfluous branches prune.
                                                  --Waller.
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   3. To preen; to prepare; to dress. --Spenser.
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            His royal bird
            Prunes the immortal wing and cloys his beak. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Pruning \Prun"ing\, n.
   1. The act of trimming, or removing what is superfluous.
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   2. (Falconry) That which is cast off by bird in pruning her
      feathers; leavings. --Beau. & Fl.
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   Pruning hook, or Pruning knife, cutting instrument used
      in pruning trees, etc.

   Pruning shears, shears for pruning trees, vines, etc.
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WordNet (r) 3.0 (2006):

pruning
    n 1: something that has been pruned off of a plant
    2: the act of trimming a plant