A fire boosted by this roars (7)

I believe the answer is:

bellows

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'this roars' is the definition.
('bellow' can be a synonym of 'roar')

I can't explain the rest of the clue.

(Other definitions for bellows that I've seen before include "shouts belligerently" , "Roars at part of the organ" , "Accordion part" , "sings very loudly" , "Fan of fire" .)

I've seen this clue in The Independent.

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