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. [1913 Webster]
Cactus wren(Zoöl.), an American wren of the genus Campylorhynchus, of several species.
cactus, n. (pl. cacti or cactuses) any succulent plant of the family Cactaceae, with a thick fleshy stem, usu. spines but no leaves, and brilliantly coloured flowers.
Idiom
cactus dahlia any kind of dahlia with quilled petals resembling a cactus flower.