costly

[kawst-lee, kost-] /ˈkɔst li, ˈkɒst-/
adjective, costlier, costliest.
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.
Origin
1350–1400; Middle English costli. See cost, -ly
Related forms
costliness, noun
overcostliness, noun
overcostly, adjective
uncostly, adjective
Synonyms
1. dear, high-priced. See expensive.
British Dictionary definitions for un costly
costly (ˈkɒstlɪ)
 
adj , -lier, -liest
1.  of great price or value; expensive
2.  entailing great loss or sacrifice: a costly victory
3.  splendid; lavish
 
'costliness
 
n

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for un costly
costly
late 14c., from cost + -ly. Earlier formation with the same sense were costful (mid-13c.), costious (mid-14c.).
Online Etymology Dictionary, © 2010 Douglas Harper
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