Opening different list (4)
I believe the answer is:
slit
'opening' is the definition.
(slit is a kind of opening)
'different list' is the wordplay.
'different' indicates anagramming the letters.
'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" .)