Assume the end of the road's ahead (3)
I believe the answer is:
don
'assume' is the definition.
(I know that assume can be written as don)
'end of the road's ahead' is the wordplay.
'end of the' suggests the final letters.
'ahead' becomes 'on' (synonyms).
The final letter of 'road' is 'd'.
'd'+'on'='DON'
'the' acts as a link.
(Other definitions for don that I've seen before include "A mafia chief or Spanish grandee" , "Put on clothes like noss" , "A Spanish grandee like Quixote" , "Mafia chief or Spanish title" , "River, academic" .)