Crossword Genius

Hydrogen air-locks (4)

Ross

I believe the answer is:

hair

'locks' is the definition.
(thesaurus)

'hydrogen air' is the wordplay.
'hydrogen' becomes 'h' (H is the chemical symbol for hydrogen).
'h'+'air'='HAIR'

(Other definitions for hair that I've seen before include "Barber's speciality; musical" , "It grows from a follicle" , "Threadlike growth" , "Barnet" , "It grows from the skin" .)

I've seen this clue in The Telegraph.
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