Definition of rainbow cactus in US English:

rainbow cactus

noun

  • Each of three small cylindrical cacti of south-western North America, Echinocereus pectinatus, E. rigidissimus, and E. dasyacanthus, which have red, pink, or yellow flowers and alternating rows of pinkish and grey-white spines creating a banded appearance.

Origin

Mid 19th century; earliest use found in Dawson's Fort Wayne (Indiana) Daily Times.