sealant (n.)

c. 1200, selen, "to fasten (a letter, etc.) with or as with a seal, close up with a seal, press a seal on wax," also "place a seal on (a document)," also figurative, "to join together," from seal (n.1) or else from Old French seeler, sealer.

Hence "to conclude, ratify, render official or binding" by affixing seals to it (late 15c.). In reference to jars or other containers, "to close up with wax, lead, cement, etc.," attested from 1660s, from the notion of wax seals on envelopes. In reference to the actions of wood-coatings, "render impervious," by 1940. Related: Sealed; sealing.

Sealing-wax, "soft substance prepared for receiving the impression of a seal," is attested from c. 1300. To seal (one's) lips "be silent" is by 1782. To seal (one's) fate (1799) "decide irrevocably" perhaps reflects the notion of a seal on a warrant of execution.

agent or instrumental suffix, from Old French and French -ant, from Latin -antem, accusative of -ans, present-participle suffix of many Latin verbs. Compare -ance.