Scot's wet-weather cover (4)
I believe the answer is:
macs
'scot's wet-weather cover' is the definition.
I can't judge whether this definition defines the answer.
'scot's wet-weather cover' is the wordplay.
'scot' becomes 'mac' (many Scottish surnames begin with Mac).
'wet weather cover' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'mac'+'s'='MACS'
Can you help me to learn more?
(Another definition for macs that I've seen is " Clothing".)