Definition of seal noun from the Oxford Advanced Learner's Dictionary

seal

noun

siːl

siːl

official mark

1 [countable] an official design or mark, stamped on a document to show that it is genuine and carries the authority of a particular person or organizationThe letter bore the president's seal.

making something definite

2 [singular] a thing that makes something definiteThe project has been given the government's seal of approval (= official approval).I looked upon the gift as a seal on our friendship.

on containers

3 [countable] a substance, strip of material, etc. used to fill a crack so that air, liquid, etc. cannot get in or outa jar with a rubber seal in the lidOnly drink bottled water and check the seal isn't broken.

on letters/boxes

4 [countable] a piece of wax (= a soft substance produced by bees ), soft metal or paper that is placed across the opening of something such as a letter or box and which has to be broken before the letter or box can be openedHe broke the wax seal and unrolled the paper.5 [countable] a piece of metal, a ring, etc. with a design on it, used for stamping a wax or metal seal

sea animal

6 [countable] a sea animal that eats fish and lives around coasts. There are many types of seal, some of which are hunted for their fura colony of sealsgrey seals basking on the rocksThe annual seal hunt takes place on the pack ice off Greenland.

Idioms

set the seal on something

(formal) to make something definite or completeHer election to the premiership set the seal on a remarkable political career.

under seal

(formal) (of a document) in a sealed envelope that cannot be opened before a particular time