Firmly resolved (4,3)
I believe the answer is:
dead set
'firmly resolved' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dead set that I've seen before include "Absolutely determined, bent on" , "A determined attack, sounds moribund" , "A determined attack - from extinct group?" , "Complete standstill; sedated (anag.)" , "Bent on - sedated (anag)" .)