/ Dictionary / Index C crookesite: Meaning and Definition of Find definitions for: crookes•ite Pronunciation: (krook'sīt), [key] — n. a rare mineral, selenide of copper, thallium, and silver, (Cu, Tl, Ag)Se, occurring in steel-gray, compact masses. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Crookes dark space Crookes radiometer Related Content Daily Word Quiz: foliage Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language