The most common and most likely answer to this crossword clue is the 9 letter word DUMBFOUND
I've seen this crossword clue in The Times
D
U
M
B
F
O
U
N
D
More clues leading to the result DUMBFOUND
Buddy explains!

The straight part
We know that "floor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case floor = dumbfound.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DUMBFOUND mean?
DUMBFOUND verb- To confuse and bewilder; to leave speechless.