/ Dictionary / Index U uracil: Meaning and Definition of Find definitions for: u•ra•cil Pronunciation: (yoor'u-sil), [key] — n. a pyrimidine base, CHNO, that is one of the fundamental components of RNA, in which it forms base pairs with adenine. Symbol: U Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: uracil (Thesaurus) Ur uraemia Related Content Daily Word Quiz: apogee Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language