Fill house (3)
I believe the answer is:
pad
This could be a double definition.
'fill' is the first definition.
(I know that pad is a type of fill)
'house' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for pad that I've seen before include "Cushion" , "Absorbent material" , "wearing this?" , "protection for member" , "Sheets of paper fastened together along one edge" .)