Hot air is naturally thin (4)

I believe the answer is:

hair

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'naturally thin' is the definition.
I can't tell whether this defines the answer.

'hot air' is the wordplay.
'hot' becomes 'h'.
'h'+'air'='HAIR'

'is' is the link.

Can you help me to learn more?

(Other definitions for hair that I've seen before include "Fibre; small extent" , "Fuzz" , "It grows from the skin" , "Coiffure" , "Fur - mop" .)

I've seen this clue in the Evening Standard.

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