any of numerous succulent plants of the family Cactaceae, of warm, arid regions of the New World, having fleshy, leafless, usually spiny stems, and typically having solitary, showy flowers.
cac·tus (kāk'təs) n.
pl.cac·ti (-tī') or cac·tus·es
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.