Extremely healthy, or OK (4,4)
I believe the answer is:
very well
This clue is a double definition.
'extremely healthy' is the first definition.
(I've seen this before)
'ok' is the second definition.
('very well' can be a synonym of 'ok')
'or' is the link.
(Other definitions for very well that I've seen before include "I agree" , "In the pink - all right then" , "Exceedingly healthy'" , "okay" , "Better than just OK" .)