Door opening in refectory accesses new canteen (8)
I believe the answer is:
entrance
'door' is the definition.
(I've seen this before)
'opening in refectory accesses new canteen' is the wordplay.
'opening in' says to take the initial letters.
'accesses' is an insertion indicator (inserted letters gain access).
'new' indicates an anagram.
The initial letter of 'refectory' is 'r'.
'canteen' anagrammed gives 'entance'.
'r' put into 'entance' is 'ENTRANCE'.
(Other definitions for entrance that I've seen before include "Fill with wonder, door" , "Way in - hypnotise" , "lobby?" , "Enchant" , "appearance" .)