Complaint uniting two females (6)
I believe the answer is:
malady
'complaint' is the definition.
(thesaurus)
'two females' is the wordplay.
'two females' can mean two substitutions for 'female'.
'female' becomes 'ma' (I can't justify this - if you can you should give a lot more credence to this answer).
'female' becomes 'lady' (lady is a kind of female).
'ma'+'lady'='MALADY'
'uniting' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
(Other definitions for malady that I've seen before include "Sickness, ailment" , "Disease, ailment" , "Illness or disease" , "Disease or disorder" , "hay fever, perhaps" .)