A horse's refusal, we hear (5)
I believe the answer is:
neigh
'a horse's' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'refusal we hear' is the wordplay.
'refusal' becomes 'nay' (archaic word for 'no').
'we hear' indicates a 'sounds like' (homophone) clue.
'nay' sounds like 'NEIGH'.
Can you help me to learn more?
(Other definitions for neigh that I've seen before include "Whinnying noise" , "Sound coming from Ben Nevis" , "Equine utterance" , "one made by Bucephalus?" , "Mare's cry, e.g." .)