seal 1 
(sēl)
(sēl)n.
1.
a. A device or material that is used to close off or fasten an opening or connection, especially to prevent the escape of a liquid or gas: used caulk as a seal around the window.
b. An airtight closure: a door that lacks a tight seal.
c. Something, such as a piece of tape, that is placed on a product or package to show that the contents have not been tampered with.
d. The water in the trap of a drain that prevents sewer gas from escaping into a room.
2.
a. A design used to identify a person or thing or to show that something is authentic, accurate, or of good quality: The title page is marked with the publisher's seal. Does the scale have the inspector's seal?
b. A small decorative paper sticker.
3.
a. A die or signet having a raised or incised emblem used to stamp an impression on a receptive substance such as wax or lead.
b. The impression so made.
c. The design or emblem itself, belonging exclusively to the user: a monarch's seal.
d. A small disk or wafer of wax, lead, or paper bearing such an imprint and affixed to a document to prove authenticity or to secure it.
4. An indication or symbol regarded as guaranteeing or authenticating something: The choral director gave the program his seal of approval.
tr.v. sealed, seal·ing, seals
Idioms: 1.
a. To close or fasten with a seal: seal an envelope; seal a test tube.
b. To prevent (a liquid or gas) from escaping: Charring a piece of meat seals in the juices.
c. To cover, secure, or fill up (an opening): sealed the hole in the pipe with epoxy.
d. To apply a waterproof coating to: seal a blacktop driveway.
e. To secure or prevent passage into and out of (an area). Often used with off: The police sealed off the crime scene.
2. To affix a seal to (something) in order to prove authenticity, accuracy, or quality.
3. To establish or determine irrevocably: Our fate was sealed.
4. Mormon Church To make (a marriage, for example) eternally binding; solemnize forever.
(one's) lips are sealed
Used to indicate that one will not disclose a piece of information.
under seal
Having an impression or emblem attesting to a document's authenticity and reliability.
[Middle English, die or signet for stamping an impression, from Old French seel, from Vulgar Latin *sigellum, from Latin sigillum, diminutive of signum, sign, seal; see sekw-1 in the Appendix of Indo-European roots.]
seala·ble adj.