Setter using extremely gauche, outdated language (7)
I believe the answer is:
gelatin
'setter' is the definition.
(substance which sets or hardens)
'extremely gauche outdated language' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'outdated language' becomes 'latin' (Latin is an example. I am not sure about the 'outdated' bit.).
'gauche' with its middle removed is 'ge'.
'ge'+'latin'='GELATIN'
'using' is the link.
Can you help me to learn more?
(Other definitions for gelatin that I've seen before include "Colourless protein extracted from animal bones" , "Colourless glue" , "Thickener" , "Animal protein used in foods, glues, emulsions, etc" , "Setter" .)