Probe about Caesar's language is widening (8)
I believe the answer is:
dilating
'widening' is the definition.
(dilating is a kind of widening)
'probe about caesar's language' is the wordplay.
'probe' becomes 'dig' (I can't explain this - if you can you should believe this answer much more).
'about' means one lot of letters goes inside another.
'caesar's language' becomes 'latin' (I've seen this before).
'dig' placed around 'latin' is 'DILATING'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for dilating that I've seen before include "Becoming expansive" , "Becoming wider" , "Swelling out or enlarging" , "Swelling or expanding" .)