Tin seen to damage tongue (9)
I believe the answer is:
cantonese
'tongue' is the definition.
(Cantonese is an example)
'tin seen to damage' is the wordplay.
'tin' becomes 'can' (synonyms).
'damage' indicates an anagram (I've seen 'damaged' mean this).
'seen'+'to'='seento'
'seento' with letters rearranged gives 'tonese'.
'can'+'tonese'='CANTONESE'
(Other definitions for cantonese that I've seen before include "Eastern language" , "tongue" , "such food?" , "Oriental" , "Chinese language" .)