Irish tongue (4)
I believe the answer is:
erse
'irish tongue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for erse that I've seen before include "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Old Gaelic for the seer" , "Old name for Celtic languages" , "Celtic tongue" , "Possibly the language" .)