Favouring just three letters out of the nine (3)

I believe the answer is:

for

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'favouring' is the definition.
(to be 'for' something is to be in favour of it)

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

(Other definitions for for that I've seen before include "On behalf of" , "Favouring" , "In favour of; since" , "Approving" , "See 24" .)

I've seen this clue in the Evening Standard.

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