Language in another series (4)
I believe the answer is:
erse
'language' is the definition.
(historical term for Scottish Gaelic)
'in another series' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ERSE' is hidden within 'another series'.
(Other definitions for erse that I've seen before include "Old language spoken by strange seer" , "Irish Gaelic language" , "Possibly the language" , "Old Scots or Irish Gaelic" , "Old Celtic language" .)