Doctor let ma in for complaint (7)
I believe the answer is:
ailment
'complaint' is the definition.
(synonyms)
'doctor let ma in' is the wordplay.
'doctor' indicates anagramming the letters.
'let'+'ma'+'in'='letmain'
'letmain' anagrammed gives 'AILMENT'.
'for' is the link.
(Other definitions for ailment that I've seen before include "infirmity" , "Complaint, affliction" , "Physical disorder" , "Minor illness" , "Slight but persistent illness" .)