End of trying — I have to yield (4)
I believe the answer is:
give
'to yield' is the definition.
('give' can be a synonym of 'yield')
'end of trying i have' is the wordplay.
'end of' indicates one should take the final letters.
'i have' becomes 'ive' (contraction of 'I have').
The last letter of 'trying' is 'g'.
'g'+'ive'='GIVE'
(Other definitions for give that I've seen before include "There's lead" , "Supply; elasticity" , "Offer, elasticity" , "Yield - supply" , "Award" .)