One who is just sitting on a bench (10)
I believe the answer is:
magistrate
'one who' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'is just sitting on a bench' is the wordplay.
I cannot really see how this works, but
'is' is found in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is found in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for magistrate that I've seen before include "Capital of Ethiopia" , "one on the bench" , "Person in court" , "Court head" , "Judge" .)