Yield a plant ovule, we hear (4)
I believe the answer is:
cede
'yield' is the definition.
(I know that yield can be written as cede)
'a plant ovule we hear' is the wordplay.
'a plant ovule' becomes 'seed' (I've seen this in another clue).
'we hear' shows a homophone (sound like).
'seed' sounds like 'CEDE'.
(Other definitions for cede that I've seen before include "Transfer" , "Give up (eg, power)" , "Give up rights or possession" , "Reluctantly give up" , "Surrender or grant" .)