cactus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of numerous succulent, spiny, usually leafless plants of the family Cactaceae, native chiefly to arid regions of the Americas, having variously colored, often showy flowers with numerous stamens and petals.
• noun Any of several similar plants.

from The Century Dictionary.

• noun The old and Linnean name for the group of plants, considered a single genus, which now form the order Cactaceæ.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.
• noun (Zoöl.) an American wren of the genus Campylorhynchus, of several species.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines