Plural of flatness; multiple instances or qualities of being flat or lacking expression.
Regular plural of 'flatness' with '-es' suffix (flatness → flatnesses), following standard English pluralization of '-ness' nouns.
It's interesting that you can count different kinds of flatness—the flatnesses of a desert, a personality, and a musical note are all different, showing how one word can describe physical, emotional, and sensory flatness!
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