Caesar's language (5)
I believe the answer is:
latin
'caesar's language' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for latin that I've seen before include "Language of old 8 down" , "and 15 Down: Student area of Paris" , "Shakespeare's was small, according to Jonson" , "Hispanic, for example" , "A Romance language" .)