Secret society member criminal men so fear (9)
I believe the answer is:
freemason
'secret society member' is the definition.
(the Freemasons are a secret society)
'criminal men so fear' is the wordplay.
'criminal' indicates an anagram.
'men'+'so'+'fear'='mensofear'
'mensofear' anagrammed gives 'FREEMASON'.
(Other definitions for freemason that I've seen before include "secret society member" , "lodger?" , "One on the square" , "Forenames (anag)" , "Fellow following secret order" .)