Preoccupation in gangland brothers, it's said (5)
I believe the answer is:
craze
'preoccupation' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for craze that I've seen before include "Fine crack" , "passing fashion" , "Mania" , "passion" , "latest thing" .)