What does "watermelon" mean?

Watermelon: 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.