Crossword Genius

Graduate and dimwit split key component (6)

Ross

I believe the answer is:

banana

I'm a little stuck... Click here to teach me more about this clue!

'split key component' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'graduate and dimwit' is the wordplay.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'and' means one lot of letters go next to another.
'dimwit' becomes 'nana' (I can't justify this - if you can you should believe this answer much more).
'ba'+'nana'='BANANA'

Can you help me to learn more?

(Other definitions for banana that I've seen before include "Fruit grown in hands" , "Fruity type" , "One out of hand" , "Elongated edible fruit" , "Sub-tropical fruit" .)

I've seen this clue in The Guardian.
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