Setter for example served up old language (7)
I believe the answer is:
gelatin
'setter' is the definition.
(substance which sets or hardens)
'example served up old language' is the wordplay.
'example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'served up' says the letters should be written backwards (in a down clue, going upwards).
'old language' becomes 'Latin' (Latin is a dead language).
'eg' reversed gives 'ge'.
'ge'+'latin'='GELATIN'
'for' acts as a link.
(Other definitions for gelatin that I've seen before include "Substance used in glue and cooking" , "Glue made from animal extracts" , "Jelling agent" , "Thickener" , "Animal protein used in foods, glues, emulsions, etc" .)