Founder of Stoicism (4)
I believe the answer is:
'founder of stoicism' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for zeno that I've seen before include "Gr. philosopher of Elea" , "Gr. philosopher (-'s paradoxes); zone (anag.)" , "Old mathematician" , "Greek philosopher of paradox fame" , "Greek philosopher of Elea (paradoxes)" .)