Open lock and take out a casual top (4-4)
I believe the answer is:
polo-neck
'top' is the definition.
(I know that polo neck is a type of sweater)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for polo-neck that I've seen before include "High close-fitting collar" , "A high turned-over collar on a jumper" , "Style of sweater collar" , "Type of jumper" , "Pullover, high turned collar" .)