Opener dropped on one, relieved initially (4)
I believe the answer is:
door
'opener' is the definition.
(I've seen this before)
'dropped on one relieved initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'dropped on one relieved' is 'DOOR'.
(Other definitions for door that I've seen before include "Means of exit and entrance" , "Usual entrance" , "Moveable structure at an entrance" , "Alternative to knocker" , "Portal" .)