City in charge of arrow poison (6)
I believe the answer is:
curare
'arrow poison' is the definition.
(I've seen this before)
'city in charge' is the wordplay.
'city' becomes 'ur'.
'in' means one lot of letters goes inside another.
'charge' becomes 'care' ('care' can be a synonym of 'charge'**).
'ur' going into 'care' is 'CURARE'.
'of' acts as a link.
(Other definitions for curare that I've seen before include "Poison used on darts" , "Arrow poison" , "Poison put on arrows" , "Paralysing plant poison" , "Poison applied to darts" .)