Seaman's waterproof coat (3)
I believe the answer is:
tar
I believe this is a double definition.
'seaman's' is the first definition.
(Jack Tar is an informal term for a sailor)
'waterproof coat' is the second definition.
(water-resistant covering for roads)
(Other definitions for tar that I've seen before include "Kind of rat for sailor" , "Thick, sticky liquid distilled from coal" , "Sticky substance - seaman" , "Black substance in cigarettes" , "Black coat" .)