Language in another sentence (4)
'language' is the definition.
(Erse is an example)
'in another sentence' is the wordplay.
'in' says the answer is hidden in the clue.
'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".)