In best of health? Agreed (4,4)
I believe the answer is:
very well
'agreed' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for very well that I've seen before include "Agreed" , "Outstandingly" , "In excellent health - all right" , "Phrase indicating compliance or assent" , "Enjoying great health" .)