An elastomeric material with adhesive qualities that is applied between components of a similar or dissimilar nature to provide an effective barrier against the passage of snow, rainwater, wind, etc.
Merriam-Webster Online Dictionarysealant (noun)
a agent - sealing a radiator sealant
a plastic material applied to parts of teeth with imperfections (as pits and fissures) to prevent dental decay
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Sealant is a substance used to block the passage of fluids through the surface or joints or openings in materials, a type of mechanical seal. In building construction sealant is sometimes synonymous with caulking and also serve the purposes of blocking dust, sound and heat transmission. Sealants may be weak or strong, flexible or rigid, permanent or temporary. Sealants are not adhesives but some have adhesive qualities and are called adhesive-sealants or structural sealants.