Opening different list (4)
I believe the answer is:
slit
'opening' is the definition.
(I know that slit is a type of opening)
'different list' is the wordplay.
'different' indicates anagramming the letters (letters placed in a different order).
'list' with letters rearranged gives 'SLIT'.
(Other definitions for slit that I've seen before include "Long narrow opening" , "Long narrow cut" , "Narrow aperture" , "Long straight cut" , "Narrow rent" .)