The Collaborative International Dictionary of English v.0.48:

Seal \Seal\ (s[=e]l), n. [OE. sele, AS. seolh; akin to OHG.
   selah, Dan. sael, Sw. sj[aum]l, Icel. selr.] (Zool.)
   Any aquatic carnivorous mammal of the families Phocidae and
   Otariidae.
   [1913 Webster]

   Note: Seals inhabit seacoasts, and are found principally in
         the higher latitudes of both hemispheres. There are
         numerous species, bearing such popular names as sea
         lion, sea leopard, sea bear, or ursine seal,
         fur seal, and sea elephant. The bearded seal
         (Erignathus barbatus), the hooded seal (Cystophora
         cristata), and the ringed seal (Phoca foetida), are
         northern species. See also Eared seal, Harp seal,
         Monk seal, and Fur seal, under Eared, Harp,
         Monk, and Fur. Seals are much hunted for their
         skins and fur, and also for their oil, which in some
         species is very abundant.
         [1913 Webster]

   Harbor seal (Zool.), the common seal (Phoca vitulina). It
      inhabits both the North Atlantic and the North Pacific
      Ocean, and often ascends rivers; -- called also marbled
      seal, native seal, river seal, bay seal, land
      seal, sea calf, sea cat, sea dog, dotard,
      ranger, selchie, tangfish.
      [1913 Webster]

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.
      [1913 Webster]

   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.
      [1913 Webster]

            Till thou canst rail the seal from off my bond
            Thou but offend'st thy lungs to speak so loud.
                                                  --Shak.
      [1913 Webster]

   3. That which seals or fastens; esp., the wax or wafer placed
      on a letter or other closed paper, etc., to fasten it.
      [1913 Webster]

   4. That which confirms, ratifies, or makes stable; that which
      authenticates; that which secures; assurance. "Under the
      seal of silence." --Milton.
      [1913 Webster]

            Like a red seal is the setting sun
            On the good and the evil men have done.
                                                  --Longfellow.
      [1913 Webster]

   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.
      [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Seal \Seal\, v. t. [imp. & p. p. Sealed; p. pr. & vb. n.
   Sealing.] [OE. selen; cf. OF. seeler, seieler, F. sceller,
   LL. sigillare. See Seal a stamp.]
   1. To set or affix a seal to; hence, to authenticate; to
      confirm; to ratify; to establish; as, to seal a deed.
      [1913 Webster]

            And with my hand I seal my true heart's love.
                                                  --Shak.
      [1913 Webster]

   2. To mark with a stamp, as an evidence of standard
      exactness, legal size, or merchantable quality; as, to
      seal weights and measures; to seal silverware.
      [1913 Webster]

   3. To fasten with a seal; to attach together with a wafer,
      wax, or other substance causing adhesion; as, to seal a
      letter.
      [1913 Webster]

   4. Hence, to shut close; to keep close; to make fast; to keep
      secure or secret.
      [1913 Webster]

            Seal up your lips, and give no words but "mum".
                                                  --Shak.
      [1913 Webster]

   5. To fix, as a piece of iron in a wall, with cement,
      plaster, or the like. --Gwilt.
      [1913 Webster]

   6. To close by means of a seal; as, to seal a drainpipe with
      water. See 2d Seal, 5.
      [1913 Webster]

   7. Among the Mormons, to confirm or set apart as a second or
      additional wife. [Utah, U.S.]
      [1913 Webster]

            If a man once married desires a second helpmate . .
            . she is sealed to him under the solemn sanction of
            the church.                           --H.
                                                  Stansbury.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Seal \Seal\, v. i.
   To affix one's seal, or a seal. [Obs.]
   [1913 Webster]

         I will seal unto this bond.              --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seal
    n 1: fastener consisting of a resinous composition that is
         plastic when warm; used for sealing documents and parcels
         and letters [syn: sealing wax, seal]
    2: a device incised to make an impression; used to secure a
       closing or to authenticate documents [syn: seal, stamp]
    3: the pelt or fur (especially the underfur) of a seal; "a coat
       of seal" [syn: seal, sealskin]
    4: a member of a Naval Special Warfare unit who is trained for
       unconventional warfare; "SEAL is an acronym for Sea Air and
       Land" [syn: Navy SEAL, SEAL]
    5: a stamp affixed to a document (as to attest to its
       authenticity or to seal it); "the warrant bore the sheriff's
       seal"
    6: an indication of approved or superior status [syn: cachet,
       seal, seal of approval]
    7: a finishing coat applied to exclude moisture
    8: fastener that provides a tight and perfect closure
    9: any of numerous marine mammals that come on shore to breed;
       chiefly of cold regions
    v 1: make tight; secure against leakage; "seal the windows"
         [syn: seal, seal off]
    2: close with or as if with a seal; "She sealed the letter with
       hot wax" [ant: unseal]
    3: decide irrevocably; "sealing dooms"
    4: affix a seal to; "seal the letter"
    5: cover with varnish [syn: varnish, seal]
    6: hunt seals

The Free On-line Dictionary of Computing (19 January 2023):

SEAL

   Semantics-directed Environment Adaptation Language.

   (ftp://ftp.cwi.nl/pub/gipe/0092b.ps.Z).


The Devil's Dictionary (1881-1906):

SEAL, n.  A mark impressed upon certain kinds of documents to attest
their authenticity and authority.  Sometimes it is stamped upon wax,
and attached to the paper, sometimes into the paper itself.  Sealing,
in this sense, is a survival of an ancient custom of inscribing
important papers with cabalistic words or signs to give them a magical
efficacy independent of the authority that they represent.  In the
British museum are preserved many ancient papers, mostly of a
sacerdotal character, validated by necromantic pentagrams and other
devices, frequently initial letters of words to conjure with; and in
many instances these are attached in the same way that seals are
appended now.  As nearly every reasonless and apparently meaningless
custom, rite or observance of modern times had origin in some remote
utility, it is pleasing to note an example of ancient nonsense
evolving in the process of ages into something really useful.  Our
word "sincere" is derived from _sine cero_, without wax, but the
learned are not in agreement as to whether this refers to the absence
of the cabalistic signs, or to that of the wax with which letters were
formerly closed from public scrutiny.  Either view of the matter will
serve one in immediate need of an hypothesis.  The initials L.S.,
commonly appended to signatures of legal documents, mean _locum
sigillis_, the place of the seal, although the seal is no longer used
-- an admirable example of conservatism distinguishing Man from the
beasts that perish.  The words _locum sigillis_ are humbly suggested
as a suitable motto for the Pribyloff Islands whenever they shall take
their place as a sovereign State of the American Union.