Sure fit (4,4)
I believe the answer is:
very well
'sure' is the definition.
(thesaurus)
'fit' is the wordplay.
I cannot really understand how this works, but
'fit' could be 'well' (associated in meaning) and 'well' is located in the answer.
The remaining letters 'very' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for very well that I've seen before include "All right, an expression of consent" , "Probably" , "Blooming" , "Better than just OK" , "In the pink - all right then" .)