Improving (2,3,4)
I believe the answer is:
on the mend
'improving' is the definition.
(on the mend means improving after an illness)
This is all the clue.
(Other definitions for on the mend that I've seen before include "Making recovery" , "Regaining health" , "Improving in health" , "Becoming better in health" , "Recovering from an injury or illness" .)