Growing row over a speaker (9)
I believe the answer is:
'a speaker' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'growing row over' is the wordplay.
I cannot quite see how this works, but
'over' could be 'o' (cricket abbreviation) and 'o' is found within the answer.
The remaining letters 'mustache' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for moustache that I've seen before include "whiskers" , "Food trap" , "Facial hair growth" , "Facial hair on a man" , "See 1" .)