Tax office (4)

I believe the answer is:

duty

I believe this clue is a double definition.

'tax' is the first definition.
(duty is a kind of tax)

'office' is the second definition.
(thesaurus)

(Other definitions for duty that I've seen before include "Tariff" , "Tax - burden" , "Financial or work obligation" , "Service - tax - office" , "Government tax" .)

I've seen this clue in The Guardian and The Telegraph.

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