The Collaborative International Dictionary of English v.0.48:

Shortening \Short"en*ing\, n.
   1. The act of making or becoming short or shorter.
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   2. (Cookery) That which renders pastry short or friable, as
      butter, lard, etc.
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The Collaborative International Dictionary of English v.0.48:

Shorten \Short"en\, v. t. [imp. & p. p. Shortened ?; p. pr. &
   vb. n. Shortening.] [See Short, a.]
   1. To make short or shorter in measure, extent, or time; as,
      to shorten distance; to shorten a road; to shorten days of
      calamity.
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   2. To reduce or diminish in amount, quantity, or extent; to
      lessen; to abridge; to curtail; to contract; as, to
      shorten work, an allowance of food, etc.
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            Here, where the subject is so fruitful, I am
            shortened by my chain.                --Dryden.
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   3. To make deficient (as to); to deprive; -- with of.
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            Spoiled of his nose, and shortened of his ears.
                                                  --Dryden.
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   4. To make short or friable, as pastry, with butter, lard,
      pot liquor, or the like.
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   To shorten a rope (Naut.), to take in the slack of it.

   To shorten sail (Naut.), to reduce sail by taking it in.
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WordNet (r) 3.0 (2006):

shortening
    n 1: fat such as butter or lard used in baked goods
    2: act of decreasing in length; "the dress needs shortening"