The Collaborative International Dictionary of English v.0.48:

Seal \Seal\, n. [OE. seel, OF. seel, F. sceau, fr. L. sigillum a
   little figure or image, a seal, dim. of signum a mark, sign,
   figure, or image. See Sign, n., and cf. Sigil.]
   1. An engraved or inscribed stamp, used for marking an
      impression in wax or other soft substance, to be attached
      to a document, or otherwise used by way of authentication
      or security.
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   2. Wax, wafer, or other tenacious substance, set to an
      instrument, and impressed or stamped with a seal; as, to
      give a deed under hand and seal.
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            Till thou canst rail the seal from off my bond
            Thou but offend'st thy lungs to speak so loud.
                                                  --Shak.
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   3. That which seals or fastens; esp., the wax or wafer placed
      on a letter or other closed paper, etc., to fasten it.
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   4. That which confirms, ratifies, or makes stable; that which
      authenticates; that which secures; assurance. "Under the
      seal of silence." --Milton.
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            Like a red seal is the setting sun
            On the good and the evil men have done.
                                                  --Longfellow.
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   5. An arrangement for preventing the entrance or return of
      gas or air into a pipe, by which the open end of the pipe
      dips beneath the surface of water or other liquid, or a
      deep bend or sag in the pipe is filled with the liquid; a
      draintrap.
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   Great seal. See under Great.

   Privy seal. See under Privy, a.

   Seal lock, a lock in which the keyhole is covered by a seal
      in such a way that the lock can not be opened without
      rupturing the seal.

   Seal manual. See under Manual, a.

   Seal ring, a ring having a seal engraved on it, or
      ornamented with a device resembling a seal; a signet ring.
      --Shak.
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