Thanks, jock, for surfacing the road soundly (6)
I believe the answer is:
tarmac
'thanks' is the definition.
Although both the answer and definition are singular nouns, I cannot see 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 tarmac that I've seen before include "something for the road" , "Trade name for road surfacing material" , "short runway, perhaps" , "Road-surfacing material" , "Surfaced area as for planes to take off and land" .)