Making appointment as nitwit mixed double gin (9)

I believe the answer is:

assigning

'making appointment' is the definition.

'nitwit mixed double gin' is the wordplay.
I cannot quite understand how this works, but
'nitwit' could be 'ass' and 'ass' is found in the answer.
an anagram of 'gin' is 'ign' which is within the answer.
This explanation may well be incorrect...

'as' acts as a link.

I've seen this clue in The Independent.

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