Ephemeral
Part of speech: adjective
Definition: Lasting for a short period of time. Existing for only one day, as with some flowers, insects, and diseases.
Example sentence: Sound is ephemeral, fleeting, but some sort of a physical manifestation can help you hold on to it longer in time. I'm sure of this; I've always thought the sound that you make is just the tip of the iceberg, like the person that you see physically is just the tip of the iceberg as well.
Ephemeron
Part of speech: noun
Definition: something short lived or transitory