Silly but not exactly dotty (5)

I believe the answer is:

potty

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

This clue could be a double definition.

'silly' is the first definition.
(thesaurus)

'not exactly dotty' is the second definition.
'potty' can be an answer for 'dotty' (thesaurus). I'm not sure about the 'not exactly' bit.

'but' is the link.

Can you help me to learn more?

(Other definitions for potty that I've seen before include "Daft (informal)" , "sort of chamber?" , "Infant's loo" , "Bonkers" , "Crazy (colloq.)" .)

I've seen this clue in the Evening Standard.

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