Subtle quality -- or unsubtle one! (8)
I believe the answer is:
overtone
'subtle quality' is the definition.
(I've seen this before)
'unsubtle one' is the wordplay.
'unsubtle' becomes 'overt' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'overt'+'one'='OVERTONE'
'or' is the link.
Can you help me to learn more?
(Other definitions for overtone that I've seen before include "Subtle implication or connotation" , "Innuendo perhaps" , "Association" , "Nuance" , "part of harmonic series" .)