Apply asphalt (4)
I believe the answer is:
pave
'apply asphalt' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pave that I've seen before include "Put on a surface of stone slabs" , "Surface with stone etc." , "Cover with flagstones" , "Cover with flags" , "Dress with stone etc" .)