Outdo, when cured (6)
I believe the answer is:
better
This clue is a double definition.
'outdo' is the first definition.
(bettering is a kind of outdoing)
'cured' is the second definition.
(I've seen this before)
'when' acts as a link.
(Other definitions for better that I've seen before include "no longer sick" , "Superior of two alternatives" , "More competent - gambler" , "More able" , "Speculator" .)