cactus

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various succulent, spiny, usually leafless plants native mostly to arid regions of the New World, having variously colored, often showy flowers with numerous stamens and petals.
2. n. Any of several similar plants.

Century Dictionary and Cyclopedia

1. n. The old and Linnean name for the group of plants, considered a single genus, which now form the order Cactaceæ. In popular use the name (with its plural cacti) is still applied to members of this order without distinction. The cochineal cactus is the Opuntia Tuna, Nopalea cochinillifera, and other species cultivated for the cochineal insect; the hedgehog cactus, species of Echinocactus; the melon or melon-thistle cactus, species of Melocactus; the nipple cactus, species of Mamillaria; the night-blooming cactus (or night-blooming cereus), Cereus grandiflorus, and other species; the old-man cactus, Cereus senilis, etc.

Wiktionary

1. n. botany Any member of the family Cactaceae, a family of flowering New World succulent plants suited to a hot, semi-desert climate.
2. n. Any succulent plant with a thick fleshy stem bearing spines but no leaves, including euphorbs.
3. adj. Australia, slang Non-functional, broken, exhausted.

GNU Webster's 1913

1. n. (Bot.) Any plant of the order Cactacæ, as the prickly pear and the night-blooming cereus. See cereus. They usually have leafless stems and branches, often beset with clustered thorns, and are mostly natives of the warmer parts of America.

WordNet 3.0

1. n. any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines