Irish Gaelic (4)
I believe the answer is:
erse
'irish gaelic' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for erse that I've seen before include "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Irish Gaelic language" , "Old Gaelic for the seer" , "Kind of Gaelic for seer" , "Old language spoken by strange seer" .)