Moderate speed in outskirts of Canton (7)
I believe the answer is:
chasten
'moderate' is the definition.
('chasten' can be a synonym of 'moderate')
'speed in outskirts of canton' is the wordplay.
'speed' becomes 'haste' (haste is a kind of speed**).
'in' means one lot of letters goes inside another.
'outskirts of' suggests removing the centre.
'canton' with its middle taken out is 'cn'.
'haste' placed into 'cn' is 'CHASTEN'.
(Other definitions for chasten that I've seen before include "Subdue the pride of, discipline" , "Punish, purify" , "Moderate" , "Subdue - a stench (anag)" , "Subdue pride of with a stench" .)