Passing hard prune stone, with Pepe's bowels opening? (9)
I believe the answer is:
ephemeral
'passing' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ephemeral that I've seen before include "A mere help (anag) - short-lived" , "short term gain" , "Short-lived, passing quickly" , "Fugitive" , "Transitory" .)