"It's cold, hurry up" does act as a curb (7)
I believe the answer is:
chasten
'a curb' is the definition.
(thesaurus)
'it's cold hurry up' is the wordplay.
'it's cold' becomes 'C' (eg on taps).
'hurry up' becomes 'hasten' (I've seen this in another clue).
'c'+'hasten'='CHASTEN'
'does act as' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for chasten that I've seen before include "Censure severely" , "Subdue, correct by punishing" , "Moderate" , "Subdue pride of with a stench" , "Have a restraining effect on (someone)" .)