The Collaborative International Dictionary of English v.0.48:

Hoop \Hoop\, n. [OE. hope; akin to D. hoep, hoepel.]
   1. A pliant strip of wood or metal bent in a circular form,
      and united at the ends, for holding together the staves of
      casks, tubs, etc.
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   2. A ring; a circular band; anything resembling a hoop, as
      the cylinder (cheese hoop) in which the curd is pressed in
      making cheese.
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   3. A circle, or combination of circles, of thin whalebone,
      metal, or other elastic material, used for expanding the
      skirts of ladies' dresses; crinoline; -- used chiefly in
      the plural.
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            Though stiff with hoops, and armed with ribs of
            whale.                                --Pope.
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   4. A quart pot; -- so called because originally bound with
      hoops, like a barrel. Also, a portion of the contents
      measured by the distance between the hoops. [Obs.]
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   5. An old measure of capacity, variously estimated at from
      one to four pecks. [Eng.] --Halliwell.
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   Bulge hoop, Chine hoop, Quarter hoop, the hoop nearest
      the middle of a cask, that nearest the end, and the
      intermediate hoop between these two, respectively.

   Flat hoop, a wooden hoop dressed flat on both sides.

   Half-round hoop, a wooden hoop left rounding and undressed
      on the outside.

   Hoop iron, iron in thin narrow strips, used for making
      hoops.

   Hoop lock, the fastening for uniting the ends of wooden
      hoops by notching and interlocking them.

   Hoop skirt, a framework of hoops for expanding the skirts
      of a woman's dress; -- called also hoop petticoat.

   Hoop snake (Zool.), a harmless snake of the Southern United
      States (Abaster erythrogrammus); -- so called from the
      mistaken notion that it curves itself into a hoop, taking
      its tail into its mouth, and rolls along with great
      velocity.

   Hoop tree (Bot.), a small West Indian tree (Melia
      sempervirens), of the Mahogany family.
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WordNet (r) 3.0 (2006):

hoop snake
    n 1: any of various harmless North American snakes that were
         formerly believed to take tail in mouth and roll along like
         a hoop