Its driver usually has the knowledge (3)
I believe the answer is:
cab
'knowledge' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for cab that I've seen before include "An American taxi" , "Driving compartment" , "It has the authority to confiscate the proceeds of crime, in short" , "info for citizens provided here" , "Transport" .)