Melon cactus

Melon \Mel"on\ (m[e^]l"[u^]n), n. [F., fr. L. melo, for melopepo
   an apple-shaped melon, Gr. mhlope`pwn; mh^lon apple + pe`pwn
   a species of large melon; cf. L. malum apple. Cf.
   {Marmalade}.]
   [1913 Webster]
   1. (Bot.) The juicy fruit of certain cucurbitaceous plants,
      as the muskmelon, watermelon, and citron melon; also, the
      plant that produces the fruit.
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   2. (Zool.) A large, ornamental, marine, univalve shell of the
      genus {Melo}.
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   {Melon beetle} (Zool.), a small leaf beetle ({Diabrotiea
      vittata}), which damages the leaves of melon vines.

   {Melon cactus}, {Melon thistle}.
      (a) (Bot.) A genus of cactaceous plants ({Melocactus})
          having a fleshy and usually globose stem with the
          surface divided into spiny longitudinal ridges, and
          bearing at the top a prickly and woolly crown in which
          the small pink flowers are half concealed. {Melocactus
          communis}, from the West Indies, is often cultivated,
          and sometimes called {Turk's cap}.
      (b) The related genus {Mamillaria}, in which the stem is
          tubercled rather than ribbed, and the flowers
          sometimes large. See Illust. under {Cactus}.
          [1913 Webster]