Gael's language (4)
I believe the answer is:
erse
'gael's language' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for erse that I've seen before include "Old Celtic language" , "Celtic tongue" , "Possibly the language" , "Irish Gaelic language" , "Kind of Gaelic for seer" .)