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.
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            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):

sealing
    n 1: the act of treating something to make it repel water [syn:
         waterproofing, sealing]