Cut removing hospital oxygen, say (3)

I believe the answer is:

gas

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'oxygen say' is the definition.
(oxygen is a kind of gas)

I cannot understand how the rest of the clue works.

(Other definitions for gas that I've seen before include "Petrol (US)" , "natural resource" , "Idle chat" , "Eg, hydrogen" , "Domestic fuel" .)

I've seen this clue in The Times.

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