Repair your old well (7)
I believe the answer is:
healthy
'well' is the definition.
(similar in meaning)
'repair your old' is the wordplay.
'repair' becomes 'heal' (I've seen this in another clue).
'your old' becomes 'thy' ('thy' historically meant 'your').
'heal'+'thy'='HEALTHY'
(Other definitions for healthy that I've seen before include "In good shape, not ill" , "Free from infirmity or disease" , "Hale and hearty" , "In the pink" , "Fit, in sound physical shape" .)