The Collaborative International Dictionary of English v.0.48:

Purchase \Pur"chase\ (?; 48), v. t. [imp. & p. p. Purchased;
   p. pr. & vb. n. Purchasing.] [OE. purchasen, porchacen, OF.
   porchacier, purchacier, to pursue, to seek eagerly, F.
   pourchasser; OF. pour, por, pur, for (L. pro) + chacier to
   pursue, to chase. See Chase.]
   1. To pursue and obtain; to acquire by seeking; to gain,
      obtain, or acquire. --Chaucer.
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            That loves the thing he can not purchase. --Spenser.
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            Your accent is Something finer than you could
            purchase in so removed a dwelling.    --Shak.
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            His faults . . . hereditary
            Rather than purchased.                --Shak.
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   2. To obtain by paying money or its equivalent; to buy for a
      price; as, to purchase land, or a house.
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            The field which Abraham purchased of the sons of
            Heth.                                 --Gen. xxv.
                                                  10.
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   3. To obtain by any outlay, as of labor, danger, or
      sacrifice, etc.; as, to purchase favor with flattery.
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            One poor retiring minute . . .
            Would purchase thee a thousand thousand friends.
                                                  --Shak.
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            A world who would not purchase with a bruise?
                                                  --Milton.
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   4. To expiate by a fine or forfeit. [Obs.]
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            Not tears nor prayers shall purchase out abuses.
                                                  --Shak.
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   5. (Law)
      (a) To acquire by any means except descent or inheritance.
          --Blackstone.
      (b) To buy for a price.
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   6. To apply to (anything) a device for obtaining a mechanical
      advantage; to get a purchase upon, or apply a purchase to;
      as, to purchase a cannon.
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WordNet (r) 3.0 (2006):

purchasing
    n 1: the act of buying; "buying and selling fill their days";
         "shrewd purchasing requires considerable knowledge" [syn:
         buying, purchasing]