Hot gas is subject of clip (4)
I believe the answer is:
hair
'subject of clip' is the definition.
(hair may be clipped by a hair clip)
'hot gas' is the wordplay.
'hot' becomes 'h' (abbreviation eg on taps).
'gas' becomes 'air'.
'h'+'air'='HAIR'
'is' is the link.
(Other definitions for hair that I've seen before include "It grows from the skin" , "Musical with nude scenes" , "Threadlike strands growing from the skin" , "The American Tribal Love-Rock Musical (1967)" , "Outgrowth from the skin" .)