Sailor’s dark waterproof coat (3)
I believe the answer is:
tar
I believe this clue is a double definition.
'sailor's' is the first definition.
(slang term for a sailor)
'dark waterproof coat' is the second definition.
(water-resistant covering for roads)
(Other definitions for tar that I've seen before include "Viscous bituminous substance" , "Dark viscous flammable substance" , "not put on ship in proverbial case of false economy?" , "Sticky road material or informal sailor" , "Sticky stuff for a kind of sailor" .)