Setter is sinless, yet flawed (9)
I believe the answer is:
imperfect
'flawed' is the definition.
(similar in meaning)
'setter is sinless' is the wordplay.
'setter is' becomes 'I'm' (the setter is the person who set the crossword).
'sinless' becomes 'perfect' (I am not sure about this - if you are sure you should believe this answer much more).
'im'+'perfect'='IMPERFECT'
'yet' is the link.
Can you help me to learn more?
(Other definitions for imperfect that I've seen before include "Flawed, defective" , "being immature" , "seconds" , "Faulty; tense" , "Deficient" .)