Hiding tear, convinced King to admit defeat (9)
I believe the answer is:
surrender
'admit defeat' is the definition.
(to surrender is to admit defeat)
'hiding tear convinced king' is the wordplay.
'hiding' indicates putting letters inside.
'tear' becomes 'rend' (rending is a kind of tearing).
'convinced' becomes 'sure' (similar in meaning).
'king' becomes 'R' (abbreviation of Latin rex).
'rend' placed into 'sure' is 'surrende'.
'surrende'+'r'='SURRENDER'
'to' acts as a link.
(Other definitions for surrender that I've seen before include "Yield to the control of another" , "Capitulation" , "Concede" , "Capitulate, relinquish" , "Cede" .)