/ Dictionary / Index R rainbow cactus: Meaning and Definition of Find definitions for: rain'bow cac"tus Pronunciation: [key] an erect stiff cactus, Echinocereus pectinatus rigidissimus, of Arizona and Mexico, having a cylindrical body, numerous interlocking spines, and pink flowers. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Rainbow Bridge rainbow-collar Related Content Daily Word Quiz: exemplary Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language