seal
n. countablen. a sea animal with thick fur and flippers that lives in cold water. It can also mean a physical mark or sticker used to close something tightly.
n. any of several carnivorous marine mammals with flippers and a streamlined body; alternatively, a device or substance used to join two things together to prevent leakage or to prove authenticity.
The seal swam gracefully through the icy water.
Check the plastic seal on the bottle to make sure nobody opened it before you bought it.
While the biological study focused on the migration patterns of the harbor seal, the legal team worked to verify the wax seal on the original 18th-century deed.
From Middle English sel, from an inflectional form of Old English seolh, from Proto-West Germanic selh, from Proto-Germanic selhaz (compare Scots selch,selkie, North Frisian selich, Middle Dutch seel, zēle, Old High German selah, Danish sæl, Middle Low German sale, Icelandic selur), either from Proto-Indo-European selk- (“to pull”) (compare dialectal English sullow (“plough”)) or from early Proto-Finnic šülkeš (later *hülgeh, compare dialectal Finnish hylki, standard hylje, Estonian hüljes).
From Middle English sele, from Anglo-Norman seel, from Latin sigillum, a diminutive of signum (“sign”). Doublet of sigil and sigillum.
From Middle English *selen (suggested by Middle English sele (“harness; hame”)), perhaps from Old English sǣlan (“to bind”).
When referring to the animal, the plural is usually 'seals'. In the context of a tight closure, it often appears in the phrase 'airtight seal'.