seal has 8 distinct synonyms spread across 7 of its 15 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is unseal.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
fastener consisting of a resinous composition that is plastic when warm; used for sealing documents and parcels and letters
a member of a Naval Special Warfare unit who is trained for unconventional warfare
“SEAL is an acronym for Sea Air and Land”
a stamp affixed to a document (as to attest to its authenticity or to seal it)
“the warrant bore the sheriff's seal”
fastener that provides a tight and perfect closure
any of numerous marine mammals that come on shore to breed; chiefly of cold regions
close with or as if with a seal
Synonyms, antonyms and the broader and narrower relations for seal come from Princeton University’s WordNet. Full sources and licences.
“She sealed the letter with hot wax”