Language in another sentence (4)
I believe the answer is:
erse
'language' is the definition.
(historical term for Scottish Gaelic)
'in another sentence' is the wordplay.
'in' indicates a hidden word.
'ERSE' is hidden in the letters of 'another sentence'.
(Other definitions for erse that I've seen before include "Old Gaelic for the seer" , "Old Celtic language" , "Old name for Celtic languages" , "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Old language spoken by strange seer" .)