Trucker's spot (3)
I believe the answer is:
'trucker's spot' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cab that I've seen before include "vehicle" , "Organisation to collect money made from crime" , "Driver's compartment, in lorry say" , "Driving compartment" , "Taxi to hold an engine-driver" .)