/ Dictionary / Index C costly: Meaning and Definition of Find definitions for: cost•ly Pronunciation: (kôst'lē, kost'-), [key] — -li•er, -li•est. costing much; expensive; high in price: a costly emerald bracelet; costly medical care. resulting in great expense: The upkeep of such a large house is costly. resulting in great detriment: It was a costly mistake because no one ever trusted him again. of great value; very valuable; sumptuous. lavish; extravagant. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: costly (Thesaurus) cost ledger costmary Related Content Daily Word Quiz: arid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language