Yield a plant ovule, say (4)
I believe the answer is:
cede
'yield' is the definition.
(synonyms)
'a plant ovule say' is the wordplay.
'a plant ovule' becomes 'seed' (I've seen this in another clue).
'say' shows a homophone (sound like).
'seed' is a homophone of 'CEDE'.
(Other definitions for cede that I've seen before include "Surrender or yield" , "Yield formally" , "Relinquish control of" , "Surrender or relinquish possession" , "Give up (power to another)" .)