Gaelic (4)
'gaelic' is the definition.
(synonyms)
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 Celtic language" , "Old Scots or Irish Gaelic" , "Kind of Gaelic for seer" , "Possibly the language" .)
'gaelic' is the definition.
(synonyms)
This is all the clue.
(Other definitions for celtic that I've seen before include "Of a group of languages such as Gaelic and Welsh" , "The race of ancient Gaels" , "Relating to Irish, Gaelic, Manx, Welsh, etc" , "Roy Keane's team on the fringe" , "Racial of Welsh, Irish etc." .)