One who enters the services (10)
I believe the answer is:
churchgoer
'one who enters' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'services' is the wordplay.
I cannot quite see how this works, but
'services' could be 'church' (church service is a kind of service) and 'church' is found within the answer.
The remaining letters 'goer' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Another definition for churchgoer that I've seen is " Regular worshipper".)