One who goes on watch (8)
I believe the answer is:
repeater
'watch' is the definition.
(thesaurus)
'one who goes on' is the wordplay.
I cannot really understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in the answer.
The remaining letters 'peter' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for repeater that I've seen before include "Maybe watch" , "Watch - gun" , "Type of clock or firearm" , "A salesman" , "Amplifier in phone line" .)