The Collaborative International Dictionary of English v.0.48:

Concealment \Con*ceal"ment\, n. [OF. concelement.]
   1. The act of concealing; the state of being concealed.
      [1913 Webster]

            But let concealment, like a worm i' the bud,
            Feed on her damask cheek.             --Shak.
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            Some dear cause
            Will in concealment wrap me up awhile. --Shak.
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   2. A place of hiding; a secret place; a retreat frem
      observation.
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            The cleft tree
            Offers its kind concealment to a few. --Thomson.
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   3. A secret; out of the way knowledge. [Obs.]
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            Well read in strange concealments.    --Shak.
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   4. (Law) Suppression of such facts and circumstances as in
      justice ought to be made known. --Wharton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

concealment
    n 1: the condition of being concealed or hidden [syn: privacy,
         privateness, secrecy, concealment]
    2: a covering that serves to conceal or shelter something; "a
       screen of trees afforded privacy"; "under cover of darkness";
       "the brush provided a covert for game"; "the simplest
       concealment is to match perfectly the color of the
       background" [syn: screen, cover, covert, concealment]
    3: the activity of keeping something secret [syn: concealment,
       concealing, hiding]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "concealment":
   abri, air-raid shelter, airtight secrecy, asylum, bolt-hole,
   bomb shelter, bombproof, bunker, cache, cave, close secrecy,
   closeness, corner, cover, covert, coverture, cranny, crypticness,
   cubby, cubbyhole, cyclone cellar, dark corner, den, disappearance,
   discreetness, discretion, dugout, earth, evasion, evasiveness,
   fallout shelter, foxhole, funk hole, hiddenness, hideaway, hideout,
   hidey hole, hiding, hiding place, hole, hugger-mugger,
   hugger-muggery, immateriality, imperceptibility, indiscernibility,
   invisibility, lair, niche, nonappearance, nook, recess, refuge,
   retreat, safety zone, sanctuary, secrecy, secret place,
   secretiveness, secretness, shelter, stash, storm cave,
   storm cellar, subterfuge, the dark, the invisible, the unseen,
   trench, uncommunicativeness, undercovert, unperceivability,
   unseeableness, unsubstantiality, viewlessness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CONCEALMENT, contracts. The unlawful suppression of any fact or
circumstance, by one of the parties to a contract, from the other, which in
justice ought to be made known. 1 Bro. Ch. R. 420; 1 Fonbl. Eq. B. 1, c. 3,
Sec. 4, note (n); 1 Story, Eq. Jur. Sec. 207.
     2. Fraud occurs when one person substantially misrepresents or conceals
a material fact peculiarly within his own knowledge, in consequence of which
a delusion exists; or uses a device naturally calculated to lull the
suspicions of a careful man, and induce him to forego inquiry into a matter
upon which the other party has information, although such information be not
exclusively within his reach. 2 Bl. Com. 451; 3 Id. 166; Sugd. Vend. 1 to
10; 1 Com. Contr. 38; 3 B. & C. 623; 5 D. & R. 490; 2 Wheat. 183; 11 Id. 59;
1 Pet. Sup. C. R. 15, 16. The party is not bound, however, to disclose
patent defects. Sugd. Vend. 2.
     3. A distinction has been made between the concealment of latent
defects in real and personal property. For example, the concealment by an
agent that a nuisance existed in connexion with a house the owner had to
hire, did not render the lease void. 6 IV. & M. 358. 1 Smith, 400. The rule
with regard to personalty is different. 3 Camp. 508; 3 T. R. 759.
     4. In insurances, where fairness is so essential to, the contract, a
concealment which is only the effect of accident, negligence, inadvertence,
or mistake, if material, is equally fatal to the contract as if it were
intentional and fraudulent. 1 Bl. R. 594; 3 Burr. 1909. The insured is
required to disclose all the circumstances within his own knowledge only,
which increase the risk. He is not, however, bound to disclose general
circumstances which apply to all policies of a particular description,
notwithstanding they may greatly increase the risk. Under this rule, it has
been decided that a policy is void, which was obtained by the concealment
by the assured of the fact that he had heard that a vessel like his was
taken. 2 P. Wms. 170. And in a case where the assured had information of "a
violent storm" about eleven hours after his vessel had sailed, and had
stated only that "there had been blowing weather and severe storms on the
coast after the vessel had sailed" but without any reference to the
particular storm it was decided that this was a concealment, which vitiated
the policy. 2 Caines R. 57. Vide 1 Marsh. Ins: 468; Park, Ins. 276; 14 East,
R. 494; 1 John. R. 522; 2 Cowen, 56; 1 Caines, 276; 3 Wash. C. C. Rep. 138;
2 Gallis. 353; 12 John. 128.
     5. Fraudulent concealment avoids the contract. See, generally, Verpl.
on Contr. passim; Bouv. Inst. Index, h.t.; Marsh. Ins. B. 1, c. 9; 1 Bell's
Com. B. 2, pt. 3, c. 15 s. 3, Sec. 1; 1 M. & S. 517; 2 Marsh. R. 336.