Knight in Big Apple a simpleton (5)

I believe the answer is:

ninny

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'a simpleton' is the definition.
(ninny is a kind of simpleton)

'knight in big apple' is the wordplay.
'knight' becomes 'n' (chess).
'big apple' becomes 'ny' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'n'+'in'+'ny'='NINNY'

Can you help me to learn more?

(Other definitions for ninny that I've seen before include "Fool" , "dope" , "Stupid foolish person" , "not a wise man" , "Silly billy" .)

I've seen this clue in The Sun.

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