Nominally a way of working in crime (5)
I believe the answer is:
simon
'nominally a' is the definition.
I can't judge whether this defines the answer.
'way of working in crime' is the wordplay.
'way of working' becomes 'mo' (abbreviation for modus operandi).
'in' indicates putting letters inside.
'crime' becomes 'sin'.
'mo' put into 'sin' is 'SIMON'.
Can you help me to learn more?
(Other definitions for simon that I've seen before include "he says it's a game" , "One of Christ's apostles" , "- Templar, The Saint" , "- Bol'var, S. American liberator" , "Simple chap" .)