Language once used in school at Inverness? (5)
I believe the answer is:
latin
'language once' is the definition.
(ancient language)
'in school at inverness?' is the wordplay.
'in' indicates the answer is hidden within the clue.
'LATIN' is hidden within 'school at inverness'.
'used' is the link.
(Other definitions for latin that I've seen before include "The language of Virgil" , "Classical language" , "demanding subject" , "The language of old Rome" , "Cicero's tongue" .)