One responsible for a put-up job (7)
I believe the answer is:
erector
'one' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I don't see?
'a put-up job' is the wordplay.
'a put up' becomes 'erect' (I've seen this in another clue).
'job' becomes 'or' (I can't justify this - if you can you should believe this answer much more).
'erect'+'or'='ERECTOR'
'responsible for' acts as a link.
Can you help me to learn more?
(Other definitions for erector that I've seen before include "puts things up" , "Constructor" , "The individual raising" , "Muscle" , "One who puts (something) up" .)