The quality or state of being ghastly; the degree to which something is horrifying, terrifying, or causes dread and dismay.
From ghastly (adjective) plus the suffix -ness, which converts adjectives into abstract nouns expressing their quality or state. Ghastly derives from Old English roots meaning to terrify or frighten.
Ghastliness is the noun that lets us discuss horror as an abstract concept—the 'ghastliness of war' turns an adjective into a philosophical property we can analyze and discuss. This is one of English's most powerful word-building tricks.
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