Admit defeat in Pacific once denied (7)
I believe the answer is:
concede
'admit defeat' is the definition.
(I've seen this in another clue)
'in pacific once denied' is the wordplay.
'in' indicates a hidden word.
'CONCEDE' is hidden in the letters of 'pacific once denied'.
(Other definitions for concede that I've seen before include "Make admission" , "Allow - give up" , "Admit something is true" , "Make concession" , "Yield; grant" .)