To which one can be knocked down or lifted up (5)
I believe the answer is:
floor
'up' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how they can define each other.
'to which one can be knocked down or lifted' is the wordplay.
I cannot quite see how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'or' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for floor that I've seen before include "Lower limit" , "Stump" , "Knock down with force" , "Knock down; storey" , "American story" .)