Black donkey – one with a low voice (4)
I believe the answer is:
bass
'low voice' is the definition.
(I've seen this in another clue)
'black donkey' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'donkey' becomes 'ass' (ass is a term for a donkey).
'b'+'ass'='BASS'
'aeur one with a' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for bass that I've seen before include "Fish - low in pitch" , "deep in the sound" , "Low singing voice" , "Lowest adult male singing voice" , "Big percussion instrument" .)