Among bananas, a different fruit (5)
I believe the answer is:
mango
'a different fruit' is the definition.
'mango' can be an answer for 'fruit' (mango is a kind of fruit). I'm not sure about the 'a different' bit.
'among bananas' is the wordplay.
'bananas' is an anagram indicator (informal term for mad).
'among' with letters rearranged gives 'MANGO'.
(Other definitions for mango that I've seen before include "fruit tree" , "Ovoid edible fruit" , "Asian fruit" , "No, Mag has the odd fruit" , "Fleshy tropical fruit" .)