Floor with a new riddle (4)
I believe the answer is:
koan
'riddle' is the definition.
(I've seen this before)
'floor with a new' is the wordplay.
'floor' becomes 'ko' (I've seen this in other clues).
'with' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'ko'+'a'+'n'='KOAN'
(Other definitions for koan that I've seen before include "Zen riddle" , "Zen paradox; OK, no (anag.)" , "There's no reason for it" .)