A sound sort of mixture (5)
I believe the answer is:
cough
This clue might be a double definition.
'a sound sort' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'mixture' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'of' acts as a link.
Can you help me to learn more?
(Other definitions for cough that I've seen before include "Abrupt exhalation" , "Respiratory infection" , "Throat complaint" , "Confess to a crime" , "Throat infection" .)