Crossword Genius

Only an extremely rare gas (6)

Ross

I believe the answer is:

butane

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'rare gas' is the definition.
'butane' can be an answer for 'gas' (I have seen 'Flammable gas ' mean 'butane' so perhaps 'gas' could also mean 'butane'). I am not sure about the 'rare' bit.

'only an extremely' is the wordplay.
'only' becomes 'but' (but can mean only - eg 'life is but a dream').
'extremely' becomes 'e' (this might be a standard abbreviation which I don't know about).
'but'+'an'+'e'='BUTANE'

Can you help me to learn more?

(Other definitions for butane that I've seen before include "Lighter fuel" , "Inflammable gas produced from petrol" , "Bottled gas used as a fuel" , "Flammable gas in petroleum" .)

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