The quality or state of being a desert; the characteristic features that make something desert-like or barren.
From 'desert' plus the noun-forming suffix '-ness,' which creates abstract nouns describing qualities. This follows the pattern of English nouns describing states: emptiness, darkness, thickness.
The '-ness' suffix is the most productive way English creates abstract nouns, but it's interesting which concrete nouns accept it naturally. We easily say 'desertness,' but 'oceanness' or 'forestness' sound wrong—these alternative nouns (oceanic quality, forestness) evolved instead.
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