Where It Comes From
Ephemeral comes from the Greek word ephemeros, built from epi- ("on" or "for") and hemera ("day") — literally, "lasting only a day." The word entered English in the 1560s as a strictly medical term: doctors used "ephemeral fever" for a fever that ran its course in a single day, as opposed to more dangerous, longer-lasting illness.
It took until the 1630s for writers to borrow the word outside of medicine, using it for anything short-lived — and that's the meaning that stuck.
Say It Around the World
Spanish and French use this word in everyday conversation. German's "ephemer" is real and dictionary-confirmed, but leans more formal and literary than its everyday synonym "vergänglich."
The next word describes something so enormous, or so beautiful, that words actually give up trying to describe it.