Concur and get on without hollow remorse (5)
I believe the answer is:
agree
'concur' is the definition.
('agree' can be a synonym of 'concur')
'get on without hollow remorse' is the wordplay.
'get on' becomes 'age' ('age' can be a synonym of 'get on'**).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'hollow' says to hollow out the word (remove centre letters).
'remorse' with its middle taken out is 're'.
'age' enclosing 're' is 'AGREE'.
'and' is the link.
(Other definitions for agree that I've seen before include "Arrive at a settlement" , "Be of one mind" , "Go along with" , "'Birds in their little nest . . . . .'" , "Hold the same view" .)