Irregular soldier’s skill adopted by Italian city resident (8)
I believe the answer is:
partisan
'irregular' is the definition.
(associated in meaning)
'soldier's skill adopted by italian city resident' is the wordplay.
I cannot really see how this works, but
'skill' could be 'art' (both can mean a talent) and 'art' is located in the answer.
'italian' could be 'pisan' (someone from Pisa) and 'pisan' is present in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for partisan that I've seen before include "pike" , "Devotee of a cause" , "type of spear" , "Highly biased" , "champion" .)