Language in other sentence (4)
I believe the answer is:
erse
'language' is the definition.
(Erse is an example)
'in other sentence' is the wordplay.
'in' says the answer is hidden in the clue.
'ERSE' is hidden in the letters of 'other sentence'.
(Other definitions for erse that I've seen before include "Old Gaelic for the seer" , "Kind of Gaelic for seer" , "Celtic tongue" , "Irish Gaelic language" , "Old Celtic language" .)