Understood grief at home defeat to some extent (8)
I believe the answer is:
fathomed
'understood' is the definition.
(fathoming is a kind of understanding)
'grief at home defeat to some extent' is the wordplay.
'to some extent' says the answer is hidden in the clue.
'FATHOMED' is hidden in the letters of 'grief at home defeat'.
(Other definitions for fathomed that I've seen before include "Sounded" , "Got" , "Deeply understood" .)