He expanded gas (6)

I believe the answer is:

helium

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This might be a double definition.

'he' is the first definition.
(synonyms)

'expanded gas' is the second definition.
'helium' can be an answer for 'gas' (helium is a gas). I am not certain of the 'expanded' bit.

Can you help me to learn more?

(Other definitions for helium that I've seen before include "Lightest noble gas" , "Light colourless gas used in balloons" , "Second lightest element" , "Very light, inert gas" , "Floating balloon gas" .)

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