She isn't crazy all day! (5)

I believe the answer is:

madam

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'she isn't' is the definition.
The definition suggests a singular noun which matches the answer.

'crazy all day' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'all day' becomes 'am' (I can't justify this - if you can you should believe this answer much more).
'mad'+'am'='MADAM'

Can you help me to learn more?

(Other definitions for madam that I've seen before include "precocious schoolgirl?" , "How one may address a woman" , "Term of address to a woman" , "'Call Me ---' (I. Berlin)" , "Bossy girl" .)

I've seen this clue in the Evening Standard.

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