/ Dictionary / Index B burnup: Meaning and Definition of Find definitions for: burn•up Pronunciation: (bûrn'up"), [key] — n. the nuclear fuel consumed in a reactor, often measured as a percentage of the atoms of fuel that have undergone fission. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: burnup (Thesaurus) burnt umber bur oak Related Content Daily Word Quiz: tactful Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language