Support a voluntary courtesy (6)

I believe the answer is:

favour

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'support' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for favour that I've seen before include "Blessing" , "Goodwill - support" , "Prefer one over the other" , "Grace and - denotes housing granted by queen" , "Give support to - kind deed" .)

I've seen this clue in The Guardian.

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