Say back Caesar's last words to Brutus? (5)
I believe the answer is:
utter
'say' is the definition.
(to utter something is to speak or say it)
'back caesar's last words to brutus?' is the wordplay.
'back' says the letters should be written in reverse.
'last' suggests the final letters.
'words to brutus?' becomes 'ettu' (Caesar says 'et tu, Brute?' in Shakespeare's play).
The final letter of 'caesar' is 'r'.
'r'+'ettu'='rettu'
'rettu' backwards is 'UTTER'.
(Other definitions for utter that I've seen before include "Speak or say" , "talk" , "Antique offer for sale" , "Express audibly" , "Say; total" .)