Grandma's somewhat bananas (4)

I believe the answer is:

nana

'grandma's' is the definition.
(I've seen this before)

'somewhat bananas' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'NANA' can be found hidden inside 'bananas'.

(Other definitions for nana that I've seen before include "Idiot" , "Fool; Zola heroine" , "Zola tale of a courtesan" , "granny" , "Zola's heroine" .)

I've seen this clue in The Everyman puzzle in The Observer.

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