Nice and smooth, though there's a hole in it (5)
I believe the answer is:
green
'smooth though there's a hole in it' is the definition.
I can't tell whether this defines the answer.
'nice and' is the wordplay.
'nice' becomes 'gree' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' becomes 'n' (common abbreviation for 'and').
'gree'+'n'='GREEN'
Can you help me to learn more?
(Other definitions for green that I've seen before include "Consultative document" , "Naive; colour" , "like 29 [MARTIAN] , stereotypically" , "Concerned with the environment in colourful way" , "The colour of envy" .)