Illness of mother, noblewoman (6)
I believe the answer is:
malady
'illness' is the definition.
(synonyms)
'mother noblewoman' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'noblewoman' becomes 'lady' (synonyms).
'ma'+'lady'='MALADY'
'of' acts as a link.
(Other definitions for malady that I've seen before include "Sickness or disease" , "Complaint" , "Disease, ailment" , "Afflication" , "Illness or disease" .)