watermelon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An African vine (Citrullus lanatus) cultivated for its large edible fruit.
2. n. The fruit of this plant, having a hard green rind and sweet watery pink or reddish flesh.

Century Dictionary and Cyclopedia

1. n. A plant, Citrullus vulgaris (frequently named Cucumis Citrullus), or its fruit. The plant, supposed to be of Asiatic origin, is a slender trailing vine, requiring a warm soil. The fruit (a pepo) is of a spherical or usually elongated form, 1½ or 2 feet long, smooth and green, or sometimes variegated on the outside, containing within a rose-colored or sometimes yellowish pulp, pleasantly flavored, and abounding in a refreshing sweetish watery juice. The watermelon is largely cultivated in Egypt, India, China, Japan, America, southern France, and elsewhere.

Wiktionary

1. n. A plant of the species Citrullus lanatus, bearing a melon-like fruit.
2. n. The fruit of the watermelon plant, having a green rind and watery flesh that is bright red when ripe and contains black pips.
3. n. pejorative, slang An environmentalist with socialist leanings (from the similarity to the fruit, being green on the outside, and red on the inside).

GNU Webster's 1913

1. n. (Bot.) The very large ovoid or roundish fruit of a cucurbitaceous plant (Citrullus vulgaris) of many varieties; also, the plant itself. The fruit sometimes weighs many pounds; its pulp is usually pink in color, and full of a sweet watery juice. It is a native of tropical Africa, but is now cultivated in many countries. See Illust. of melon.

WordNet 3.0

1. n. large oblong or roundish melon with a hard green rind and sweet watery red or occasionally yellowish pulp
2. n. an African melon