Sailor covered in viscous substance (3)
I believe the answer is:
tar
This clue might be a double definition.
'sailor' is the first definition.
(slang term for a sailor)
'covered in viscous substance' is the second definition.
'tar' can be an answer for 'substance' (tar is a kind of substance). I am not sure about the 'covered in viscous' bit.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "Informal sailor or road-surfacing material" , "Thick, sticky liquid distilled from coal" , "Viscous liquid; sailor" , "Cigarette substance" , "Harmful tobacco residue" .)