The Collaborative International Dictionary of English v.0.48:

Avoirdupois \Av`oir*du*pois"\ ([a^]v`[~e]r*d[-u]*poiz"), n. & a.
   [OE. aver de peis, goods of weight, where peis is fr. OF.
   peis weight, F. poids, L. pensum. See Aver, n., and
   Poise, n.]
   1. Goods sold by weight. [Obs.]
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   2. Avoirdupois weight.
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   3. Weight; heaviness; as, a woman of much avoirdupois.
      [Colloq.]
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   Avoirdupois weight, a system of weights by which coarser
      commodities are weighed, such as hay, grain, butter,
      sugar, tea.
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   Note: The standard Avoirdupois pound of the United States is
         equivalent to the weight of 27.7015 cubic inches of
         distilled water at 62[deg] Fahrenheit, the barometer
         being at 30 inches, and the water weighed in the air
         with brass weights. In this system of weights 16 drams
         make 1 ounce, 16 ounces 1 pound, 25 pounds 1 quarter, 4
         quarters 1 hundred weight, and 20 hundred weight 1 ton.
         The above pound contains 7,000 grains, or 453.54 grams,
         so that 1 pound avoirdupois is equivalent to 1 31-144
         pounds troy. (See Troy weight.) Formerly, a hundred
         weight was reckoned at 112 pounds, the ton being 2,240
         pounds (sometimes called a long ton).
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WordNet (r) 3.0 (2006):

avoirdupois weight
    n 1: a system of weights based on the 16-ounce pound (or 7,000
         grains) [syn: avoirdupois, avoirdupois weight]