First known use: 1560s

From Greek ephēmeros "lasting only a day," from epi- "upon" + hēmera "day." Originally used in biology to describe organisms with very short life cycles. The word entered English via Latin ephemerus and French éphémère.

The noun sense ("a short-lived plant") dates from the 1640s. The philosophical usage referring to the transient nature of existence became prominent in 19th century Romantic literature.

📚 Fun Fact: The ancient Greeks used ephemeral tablets (ephēmerides) to record daily financial transactions — literally "day-books." The connection between "one day" and financial records highlights how the ancients viewed daily entries as temporary records.