Everything unknown disregarded by supporter (3)

I believe the answer is:

all

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'everything' is the definition.
(all things)

I can't explain the rest of the clue.

(Other definitions for all that I've seen before include "Comprising every individual one" , "The lot, everyone" , "Wholly" , "without exception" , "Straight garden path" .)

I've seen this clue in The Independent.

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