The Collaborative International Dictionary of English v.0.48:
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.
1. (Bot.) The juicy fruit of certain cucurbitaceous plants,
as the muskmelon, watermelon, and citron melon; also, the
plant that produces the fruit.
2. (Zool.) A large, ornamental, marine, univalve shell of the
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.