Convex floor's not good (5)
I believe the answer is:
round
'convex' is the definition.
(thesaurus)
'floor's not good' is the wordplay.
I cannot really understand how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
The remaining letters 'rund' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for round that I've seen before include "regular series" , "balls are like this" , "Game of golf" , "delivery trip?" , "Shaped like a circle" .)