Lower floor
I believe the answer is:
knock down
I believe this is a double definition.
'lower' is the first definition.
(thesaurus)
'floor' is the second definition.
('knock down' can be a synonym of 'floor')
(Other definitions for knock down that I've seen before include "Cheap - floor" , "Fell - to this bargain price?" , "aim of Haye, say" , "level" , "Declare (lot) sold" .)