Fruit and nuts, mostly (6)
I believe the answer is:
banana
'fruit' is the definition.
(type of fruit)
'nuts mostly' is the wordplay.
'nuts' becomes 'bananas' (as in crazy).
'mostly' means to remove the last letter.
'bananas' with its last letter taken off is 'BANANA'.
'and' is the link.
(Other definitions for banana that I've seen before include "Another of 5 down" , "Fruit led by prohibition" , "that may be unzipped" , "Curved yellow fruit" , "6 Yellow fruit" .)