His patients never say a word! (3)
I believe the answer is:
vet
'his patients never say a word' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for vet that I've seen before include "'Animal doctor, in short (3)'" , "Examine carefully - might one help a lame duck?" , "animal doctor to > investigate" , "Examine, check" , "Check someone for suitability" .)