Drug-dealers caught with millions in armed robberies (8)
I believe the answer is:
chemists
'drug-dealers' is the definition.
'caught with millions in armed robberies' is the wordplay.
'caught' becomes 'c' (cricket abbreviation**).
'with' means one lot of letters go next to another.
'millions' becomes 'm' (abbreviation).
'in' is an insertion indicator.
'armed robberies' becomes 'heists' ('heist' can be a synonym of 'armed robbery').
'm' put inside 'heists' is 'hemists'.
'c'+'hemists'='CHEMISTS'
(Other definitions for chemists that I've seen before include "Apothecaries" , "They dispense prescriptions" , "Pharmacists, say" , "pair of Boots?" , "They study elements and their compounds" .)