Fruit put in crackers? (3)
I believe the answer is:
nut
'fruit' is the definition.
(nut is a kind of fruit)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for nut that I've seen before include "buff" , "Enthusiast (slang)" , "Hard-headed person" , "Fruit with hard case" , "Head; hard fruit" .)