This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. The state or condition of being ephemeral; transience.

n. Something that is ephemeral.

n. The quality or state of being ephemeral; that which is ephemeral; a transient trifle.

n. the property of lasting for a very short time

"For an experience of the un-nameable on a colossal scale, as well as snapshots of commonplace people, one comes here, to Mr. Eisenman's memorial, where the materiality of stone competes and cooperates with the ephemerality of language and names, and where at least some of the names achieve a permanence of their own."

transitoriness    transience    transiency   

ephemeralness