The Collaborative International Dictionary of English v.0.48:

nun \nun\ (n[u^]n), n. [OE. nunne, AS. nunne, fr. L. nonna nun,
   nonnus monk; cf. Gr. ?, ?; of unknown origin. Cf. Nunnery.]
   [1913 Webster]
   1. A woman devoted to a religious life, who lives in a
      convent, under the three vows of poverty, chastity, and
      obedience.
      [1913 Webster]

            They holy time is quiet as a nun
            Breathless with adoration.            --Wordsworth.
      [1913 Webster]

   2. (Zool.)
      (a) A white variety of domestic pigeons having a veil of
          feathers covering the head.
      (b) The smew.
      (c) The European blue titmouse.
          [1913 Webster]

   Gray nuns (R. C. Ch.), the members of a religious order
      established in Montreal in 1745, whence branches were
      introduced into the United States in 1853; -- so called
      from the color or their robe, and known in religion as
      Sisters of Charity of Montreal.

   Nun buoy. See under Buoy.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Buoy \Buoy\ (bwoi or boi; 277), n. [D. boei buoy, fetter, fr.
   OF. boie, buie, chain, fetter, F. bou['e]e a buoy, from L.
   boia. "Boiae genus vinculorum tam ferreae quam ligneae."
   --Festus. So called because chained to its place.] (Naut.)
   A float; esp. a floating object moored to the bottom, to mark
   a channel or to point out the position of something beneath
   the water, as an anchor, shoal, rock, etc.
   [1913 Webster]

   Anchor buoy, a buoy attached to, or marking the position
      of, an anchor.

   Bell buoy, a large buoy on which a bell is mounted, to be
      rung by the motion of the waves.

   Breeches buoy. See under Breeches.

   Cable buoy, an empty cask employed to buoy up the cable in
      rocky anchorage.

   Can buoy, a hollow buoy made of sheet or boiler iron,
      usually conical or pear-shaped.

   Life buoy, a float intended to support persons who have
      fallen into the water, until a boat can be dispatched to
      save them.

   Nut buoy or Nun buoy, a buoy large in the middle, and
      tapering nearly to a point at each end.

   To stream the buoy, to let the anchor buoy fall by the
      ship's side into the water, before letting go the anchor.


   Whistling buoy, a buoy fitted with a whistle that is blown
      by the action of the waves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nun buoy
    n 1: a buoy resembling a cone [syn: conical buoy, nun, nun
         buoy]