Benefit ultimately debatable with money wasted - drivers' warning (4)
I believe the answer is:
toot
'benefit' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for toot that I've seen before include "Do it on a flute" , "Use horn" , "Sound of a car horn" , "Briefly blow" , "Parp" .)