Nominal mode of operating in crime (5)
I believe the answer is:
simon
'nominal mode' is the definition.
The definition suggests a singular noun which matches the answer.
'operating in crime' is the wordplay.
'operating' becomes 'mo' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'crime' becomes 'sin'.
'mo' put into 'sin' is 'SIMON'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for simon that I've seen before include "Sir -- Rattle, conductor" , "Apostle Peter's other name" , "Bolivar, de Montfort, Callow or Cowell?" , "- Templar, The Saint" , "he says it's a game" .)