As a rule, it curtails the walk back (3)
I believe the answer is:
law
'as a rule it' is the definition.
I can't judge whether this defines the answer.
'curtails the walk back' is the wordplay.
'curtails' means to remove the last letter (I've seen 'curtailed' mean this).
'back' says the letters should be written backwards.
'walk' with its last letter taken away is 'wal'.
'wal' backwards is 'LAW'.
Can you help me to learn more?
(Other definitions for law that I've seen before include "Rule, statute" , "Rule prohibiting certain actions" , "Collection of rules for a society" , "Set of rules laid down by authority" , "Body of rules of conduct for a society" .)