Some inhale, then exhale an anaesthetic (6)

I believe the answer is:

ethene

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'an anaesthetic' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'some inhale then exhale' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ETHENE' can be found hidden inside 'inhale then exhale'.

Can you help me to learn more?

(Another definition for ethene that I've seen is " Compound".)

I've seen this clue in The Hindu.

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