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Synonyms for Ephemeral (same or very similar meaning)

WordNet sense 1 (anything short-lived, as an insect that lives only for a day in its winged form):
ephemeron

WordNet sense 2 (lasting a very short time):
passing, short-lived, transient, transitory, fugacious

WordNet sense 3 (not permanent; not lasting):
temporary


From the ODE community, based on WordNetadd/edit