One starting a suit with no design, turning up fine suit (9)
I believe the answer is:
plaintiff
'one starting a' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'suit with no design turning up fine suit' is the wordplay.
I cannot quite see how this works, but
'suit' could be 'plaint' (I have seen 'Legal suit' mean 'plaint' so perhaps 'suit' could also mean 'plaint') and 'plaint' is found within the answer.
'fine' could be 'f' (abbreviation e.g. condition of old coins, books) and 'f' is found in the answer.
The remaining letters 'if' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for plaintiff that I've seen before include "Person who brings a legal action" , "Person bringing a legal action" , "accusing person in suit" , "The one taking the court action" , "One brings a legal case against another" .)