The quality or state of being fleeting; the condition of passing quickly or lasting only briefly.
From 'fleeting' (adjective) plus the noun-forming suffix '-ness,' which creates abstract nouns for qualities—a pattern combining Old English '-ness' with adjectives to name intangible characteristics.
Philosophers and poets love 'fleetingness' because it names something we all feel—the heartbreaking way good moments vanish before we can hold them, condensed into one melancholic word.
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