From the biting cold, help to protect (4)
I believe the answer is:
acid
'help to protect' is the definition.
I can't tell whether this definition defines the answer.
'from the biting cold' is the wordplay.
'from' becomes 'aid' (I can't explain this - if you can you should give a lot more credence to this answer).
'the biting' is an insertion indicator (I've seen this in other clues).
'cold' becomes 'c' (eg on taps).
'aid' going around 'c' is 'ACID'.
Can you help me to learn more?
(Other definitions for acid that I've seen before include "Sour to the taste" , "Vinegary" , "Corrosive fluid" , "Corrosive liquid; drug" , "Alkali's opposite" .)