Pronunciation: (kôst'lē, kost'-), [key]
—adj., -li•er, -li•est.
1. costing much; expensive; high in price: a costly emerald bracelet; costly medical care.
2. resulting in great expense: The upkeep of such a large house is costly.
3. resulting in great detriment: It was a costly mistake because no one ever trusted him again.
4. of great value; very valuable; sumptuous.
5. lavish; extravagant.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.