"design stamped on wax," especially an impressed figure attached to a document as evidence of authenticity, c. 1200,sel,sele, from Old Frenchseel,seal "seal on a letter" (Modern Frenchsceau), from Vulgar Latin*sigellum (source of Italiansuggello, Spanishsello; also Old Frisian and Middle High Germansigel, GermanSiegel), from Latinsigillum "small picture, engraved figure, seal," diminutive ofsignum "identifying mark, sign" (seesign (n.)).

An earlier borrowing directly from Latin is represented by Old Englishinsigel. The use for "engraved device of some hard material used for imprinting a seal" (technically amatrix) is by c. 1300. Extended senses are via the notion of a seal used to mark and close a document to insure its secrecy (c. 1300). The meaning "an identifying mark" is from mid-14c.; especially one confirming goods and measures as conforming to standard. The technical sense of "what prevents the escape of a gas or liquid" is by 1853.

"fish-eating marine mammal with flippers; any pinniped not a walrus," Middle Englishsele, from Old Englishseolh "seal," from Proto-Germanic*selkhaz (compare Old Norseselr, Swedishsjöl, Danishsæl, Middle Low Germansel, Middle Dutchseel, Old High Germanselah), a word of unknown origin, perhaps a borrowing from Finnic.

Seal point "dark brown marking on a Siamese cat" is recorded from 1934, from the resemblance to the color of seal fur; compareseal brown "rich, dark brown color," which is attested by 1875. Old Englishseolhbæð, literally "seal's bath," was an Anglo-Saxon kenning for "the sea."

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," fromseal (n.1) or else from Old Frenchseeler,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. Toseal (one's) lips "be silent" is by 1782. Toseal (one's) fate (1799) "decide irrevocably" perhaps reflects the notion of a seal on a warrant of execution.