He's loath to pay for faultless service on the motorway (5)
I believe the answer is:
miser
'he's loath to pay' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'faultless service on the motorway' is the wordplay.
'faultless service' becomes 'ser' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' says to put letters next to each other.
'the motorway' becomes 'MI' (resembles Ms, English motorway).
'ser' put after 'mi' is 'MISER'.
'for' is the link.
Can you help me to learn more?
(Other definitions for miser that I've seen before include "Avaricious hoarder" , "screw" , "Mean-minded type" , "Penny-pincher" , "Mean person" .)