ephemeral

ef-EM-er-uhl

meaning in plain English

Lasting only a very short time, gone almost as soon as it appears.

Think a one-day fly — here now, ephemeral and gone tomorrow.

for example

The rainbow was ephemeral, fading just minutes after the rain stopped.

If something is ephemeral, it does not last. Why do people chase sunsets? Because they are ephemeral — beautiful for a moment, then gone.