Spot empty mousetrap in big house (6)
I believe the answer is:
pimple
'spot' is the definition.
(I've seen this before)
'empty mousetrap in big house' is the wordplay.
'empty' suggests removing the centre.
'in' means one lot of letters goes inside another.
'big house' becomes 'pile' (term for a large or fancy house).
'mousetrap' with its middle taken out is 'mp'.
'mp' going into 'pile' is 'PIMPLE'.
(Other definitions for pimple that I've seen before include "Inflamed skin spot" , "Small pustule" .)