Organic sealant (3)
I believe the answer is:
tar
'organic sealant' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tar that I've seen before include "Harmful tobacco residue" , "prepare for feathers?" , "A sailor; a preservative" , "Dark liquid used on roads" , "Tobacco residue; sailor" .)