Talk of argon, for one (3)
I believe the answer is:
gas
I believe this is a double definition.
'talk' is the first definition.
(thesaurus)
'argon for one' is the second definition.
(argon is a kind of gas)
'of' acts as a link.
(Other definitions for gas that I've seen before include "Petrol (USA)" , "Possibly noble" , "Oxygen maybe" , "Hydrogen or oxygen, say" , "could be embarrassing for American" .)