It makes the roller wet (5)
I believe the answer is:
paint
'roller wet' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'it makes the' is the wordplay.
'it makes' becomes 'pain' (I can't justify this - if you can you should believe this answer much more).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'pain'+'t'='PAINT'
Can you help me to learn more?
(Other definitions for paint that I've seen before include "Decorative coating" , "Artist's material" , "A pint of liquid decoration" , "Coloured coating" , "Coloured liquid in tins" .)