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.
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   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.
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   3. To fasten with a seal; to attach together with a wafer,
      wax, or other substance causing adhesion; as, to seal a
      letter.
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   4. Hence, to shut close; to keep close; to make fast; to keep
      secure or secret.
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            Seal up your lips, and give no words but "mum".
                                                  --Shak.
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   5. To fix, as a piece of iron in a wall, with cement,
      plaster, or the like. --Gwilt.
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   6. To close by means of a seal; as, to seal a drainpipe with
      water. See 2d Seal, 5.
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   7. Among the Mormons, to confirm or set apart as a second or
      additional wife. [Utah, U.S.]
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            If a man once married desires a second helpmate . .
            . she is sealed to him under the solemn sanction of
            the church.                           --H.
                                                  Stansbury.
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WordNet (r) 3.0 (2006):

sealed
    adj 1: established irrevocably; "his fate is sealed" [syn:
           sealed, certain] [ant: uncertain, unsealed]
    2: closed or secured with or as if with a seal; "my lips are
       sealed"; "the package is still sealed"; "the premises are
       sealed" [ant: unsealed]
    3: undisclosed for the time being; "sealed orders"; "a sealed
       move in chess"
    4: determined irrevocably; "his fate is sealed"
    5: having been paved
    6: covered with a waterproof coating; "a sealed driveway"
    7: (of walls) covered with a coat of plaster [syn: plastered,
       sealed]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "sealed":
   able, accepted, acknowledged, admitted, affirmed, agreed, airtight,
   allowed, approved, arranged, auricular, authenticated, avowed,
   between us, certified, close, compact, compacted, conceded,
   confessed, confidential, confirmed, contracted, countersigned,
   covenanted, dustproof, dusttight, endorsed, engaged, enigmatic,
   esoteric, fast, firm, gasproof, gastight, granted, hermetic,
   hermetically sealed, in petto, incalculable, incognizable, inside,
   lightproof, lighttight, mysterious, not for publication, notarized,
   off the record, oilproof, oiltight, privileged, professed,
   promised, puzzling, rainproof, raintight, ratified, received,
   recognized, settled, shut fast, signed, smokeproof, smoketight,
   snug, stamped, staunch, stipulated, stormproof, stormtight,
   strange, sworn and affirmed, sworn to, tight, unapparent,
   unapprehended, unascertained, unbeknown, uncharted, unclassified,
   under privilege, undertaken, underwritten, undisclosed,
   undiscoverable, undiscovered, undivulged, unexplained, unexplored,
   unexposed, unfamiliar, unfathomed, unheard, unheard-of,
   unidentified, uninvestigated, unknowable, unknown, unperceived,
   unplumbed, unpublishable, unrevealed, unsuspected, untouched,
   validated, virgin, warranted, water-repellant, waterproof,
   watertight, windproof, windtight