Gangster's power with young is massive (8)
I believe the answer is:
almighty
'massive' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I don't see?
'gangster's power with young' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'power' becomes 'might' ('might' can be a synonym of 'power'**).
'with' means one lot of letters go next to another.
'young' becomes 'y'.
'al'+'might'+'y'='ALMIGHTY'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for almighty that I've seen before include "Supremely powerful" , "Excessive" , "Omnipotent; enormous" , "Supreme" , "Huge" .)