One doing a more appropriate job? (6)
I believe the answer is:
fitter
'one doing a more' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'appropriate job?' is the wordplay.
'appropriate' becomes 'fit' (similar in meaning).
'job?' becomes 'ter' (I can't explain this - if you can you should believe this answer much more).
'fit'+'ter'='FITTER'
Can you help me to learn more?
(Other definitions for fitter that I've seen before include "to get in better shape" , "Tradesman being in better shape" , "A skilled technician" , "Worker assembling machinery - more healthy" , "Assembler; more suitable" .)