I lament about illness (7)
I believe the answer is:
ailment
'illness' is the definition.
(an ailment is an illness or health problem)
'i lament about' is the wordplay.
'about' is an anagram indicator.
'i'+'lament'='ilament'
'ilament' anagrammed gives 'AILMENT'.
(Other definitions for ailment that I've seen before include "problem" , "Complaint, affliction" , "Malady" , "Slight but persistent illness" , "Bodily disorder or disease" .)