The quality or state of being expensive; the degree to which something costs a lot of money.
From 'expensive' plus the noun-forming suffix '-ness.' Both 'expensive' and '-ness' have long histories in English, dating back centuries.
While 'expensiveness' is grammatically perfect English, we often use 'cost' or 'price' instead because they're simpler. But 'expensiveness' emphasizes the quality itself—how expensive something inherently is, not just what it costs.
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