Brief film, western, shown inside (6)
I believe the answer is:
lawyer
'brief' is the definition.
(slang term for a lawyer)
'film western shown inside' is the wordplay.
'film' becomes 'layer' (film can mean a thin layer of something).
'western' becomes 'w'.
'shown inside' indicates putting letters inside.
'layer' going around 'w' is 'LAWYER'.
(Other definitions for lawyer that I've seen before include "Member of the legal profession" , "A solicitor, barrister or the like" , "One gives legal advice" , ""Let's kill all the --s" (Henry VI/2)" , "Legal specialist" .)