Sadly, mine is half full on the last day (9)

I believe the answer is:

pitifully

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'sadly' is the definition.
Both the definition and answer are adverbs. Maybe they are linked in a way I don't understand?

'mine is half full on the last day' is the wordplay.
'mine' becomes 'pit' (as in a mining pit).
'is half' indicates taking half.
'on' indicates putting letters inside.
'the last day' becomes 'illy' (I can't explain this - if you can you should believe this answer much more).
'full' cut in half is 'fu'.
'fu' put into 'illy' is 'ifully'.
'pit'+'ifully'='PITIFULLY'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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