The quality or state of being expensive or causing great expense, loss, or sacrifice.
Derived from 'costly' (adjective) plus the suffix '-ness' which forms abstract nouns. 'Costly' comes from Old English 'cost' via Norman French, ultimately from Latin. The '-ness' suffix is one of the most productive noun-forming tools in English, creating abstract qualities from adjectives.
The suffix '-ness' is so powerful in English that you can almost add it to any adjective to create a noun describing that quality—but 'costliness' is special because it suggests not just high price, but the weight and burden of expense itself.
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