May 1, lucky to be unoccupied? Very! (8)

I believe the answer is:

mightily

'very' is the definition.
(thesaurus)

'may 1 lucky to be unoccupied?' is the wordplay.
'may' becomes 'might' (synonyms).
'1' becomes 'I' (Roman numeral).
'to be unoccupied?' suggests removing the centre (I've seen 'unoccupied' mean this (remove the inside letters which occupy the word)).
'lucky' with its middle taken out is 'ly'.
'might'+'i'+'ly'='MIGHTILY'

(Another definition for mightily that I've seen is " To a very great extent".)

I've seen this clue in The Telegraph.

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