Some standing at ease for opening (4)
I believe the answer is:
gate
'for opening' is the definition.
(I have seen 'Movable opening ' mean 'gate' so perhaps 'opening' could also mean 'gate')
'some standing at ease' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'GATE' is hidden within 'standing at ease'.
(Other definitions for gate that I've seen before include "Access here" , "Total of spectators" , "Frame for closing an entrance" , "Number of people admitted to a sporting event" , "Entrance to a Dublin theatre" .)