noun

1. a design, initial, or other device placed on a letter, document, etc., as a mark of genuineness or authenticity: letters were, esp. formerly, closed with a wafer of molten wax into which was pressed the distinctive seal of the sender
2. a stamp, signet ring, etc., or the signet itself, used in making such a design
3. a wax wafer, piece of paper, etc. bearing the impression of some official design and used as to authenticate a signature or document
4. 1. something that seals, closes, or fastens tightly or securely; specif., a piece of metal, paper, etc. so placed over a lid, cap, etc. that it must be broken before the container can be opened
   2. a tight closure, as against the passage of air or water
5. anything that confirms, authenticates, or guarantees; pledge
6. an indication; sign; token a handshake as a seal of friendship
7. 1. any device preventing the passage of gas through a pipe
   2. the standing water in the trap of a drainpipe
8. ☆ an ornamental stamp placed on envelopes, packages, etc. a Christmas seal

Etymology: ME seel < OFr < L sigillum, a seal, mark, dim. of signum: see sign

transitive verb

1. to mark with a seal; fix a seal to
2. to secure the contents of (a letter, envelope, etc.), orig. by closing with a sealed wax wafer, now usually with mucilage, tape, or a gummed flap
3. to confirm or authenticate (a document, etc.) by marking with a seal
4. to attest to or confirm the truth or genuineness of (a promise, bargain, etc.)
5. to certify as being accurate, exact, of a given size, quality, capacity, etc. by fixing a stamp or seal to
6. to grant, assign, or designate with a seal, pledge, etc.
7. to settle, determine, or decide finally or irrevocably to seal one's fate
8. 1. to close, shut, or fasten with or as with a seal to seal one's lips
   2. to close completely so as to make airtight or watertight
   3. to apply a nonpermeable coating to (a porous surface, as of wood) as before painting
9. Elec. to bring (a plug and jack) into full, interlocking contact
10. ☆ Mormon Ch. to solemnize (a marriage) for eternity in a church rite

Etymology: ME selen < OFr seeler < the n.