Undertaker, perhaps, though probably not driving a hearse? (4,3)
I believe the answer is:
road hog
'undertaker' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for road hog that I've seen before include "A careless and selfish driver, the swine" , "Mr Toad, for one" , "Selfish and dangerous driver" , "Boorishly reckless driver" , "Boorish driver" .)