One lacking belief is given dabs of accessories to armed robbery (7)
I believe the answer is:
atheist
'one lacking belief is given dabs' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'accessories to armed robbery' is the wordplay.
'accessories' becomes 'at' (I can't justify this - if you can you should believe this answer much more).
'to armed robbery' becomes 'heist' (synonyms).
'at'+'heist'='ATHEIST'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for atheist that I've seen before include "One denies the existence of a god" , "One doesn't believe" , "One who does not believe in the existence of a god" , "One denying existence of a god" , "One disbelieving in the existence of God or gods" .)