Sentence:  The doctor sat down rather wearily , caressing the hen and remarking that the city was not the place for a poultry loving man , but no sooner was the remark out than a knock at this <WSD>door</WSD> obliged him to cover the hen with his greatcoat once more . 
Meaning of the word marked with <WSD> tags:  a swinging or sliding barrier that will close the entrance to a room or building or vehicle