The Collaborative International Dictionary of English v.0.48:

Covert \Cov"ert\, n. [OF. See Covert, a.]
   1. A place that covers and protects; a shelter; a defense.
      [1913 Webster]

            A tabernacle . . . for a covert from storm. --Is.
                                                  iv. 6.
      [1913 Webster]

            The highwayman has darted from his covered by the
            wayside.                              --Prescott.
      [1913 Webster]

   2. [Cf. F. couverte.] (Zool.) One of the special feathers
      covering the bases of the quills of the wings and tail of
      a bird. See Illust. of Bird.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Covert \Cov"ert\ (k?v"?rt), a. [OF. covert, F. couvert, p. p. of
   couvrir. See Cover, v. t.]
   1. Covered over; private; hid; secret; disguised.
      [1913 Webster]

            How covert matters may be best disclosed. --Shak.
      [1913 Webster]

            Whether of open war or covert guile.  --Milton
      [1913 Webster]

   2. Sheltered; not open or exposed; retired; protected; as, a
      covert nook. -- Wordsworth.
      [1913 Webster]

            Of either side the green, to plant a covert alley.
                                                  --Bacon.
      [1913 Webster]

   3. (Law) Under cover, authority or protection; as, a feme
      covert, a married woman who is considered as being under
      the protection and control of her husband.
      [1913 Webster]

   Covert way, (Fort.) See Covered way, under Covered.

   Syn: Hidden; secret; private; covered; disguised; insidious;
        concealed. See Hidden.
        [1913 Webster]

WordNet (r) 3.0 (2006):

covert
    adj 1: secret or hidden; not openly practiced or engaged in or
           shown or avowed; "covert actions by the CIA"; "covert
           funding for the rebels" [ant: open, overt]
    2: (of a wife) being under the protection of her husband; "a
       woman covert"
    n 1: a flock of coots
    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]

Moby Thesaurus II by Grady Ward, 1.0:

224 Moby Thesaurus words for "covert":
   abri, abstruse, air-raid shelter, armored, asylum, back-door,
   backstairs, beclouded, between the lines, blanket, blind,
   bolt-hole, bomb shelter, bombproof, boscage, bosket, brake, bunker,
   buried, burrow, by stealth, cache, camouflaged, canebrake, cased,
   cave, ceiled, ceja, chamisal, chaparral, clandestine, cloak,
   cloaked, close, clouded, coat, coated, concealed, concealment,
   coped, coppice, copse, copsewood, corner, couch, cover, coverage,
   covered, covering, covertly, coverture, cowl, cowled, cowling,
   cranny, cryptic, cubby, cubbyhole, curtain, curtained,
   cyclone cellar, dark corner, delitescent, den, disguised, dormant,
   drape, drapery, dugout, earth, eclipsed, encapsulated, encapsuled,
   encased, enveloped, enwrapped, esoteric, fallout shelter, feather,
   feathers, feline, filmed, floored, form, foxhole, frith, funk hole,
   furtive, furtively, guarded, guise, hackle, hanging, harbor,
   harborage, haven, hibernating, hid, hidden, hideaway, hideout,
   hidey hole, hiding, hiding place, hidlings, hole, hole-and-corner,
   hood, hooded, housed, housing, hugger-mugger, hush-hush,
   in a cloud, in a fog, in camera, in eclipse, in purdah,
   in the wings, incommunicado, lair, latent, lodge, loricate,
   loricated, lurking, mail, mantle, mantled, mask, masked, mew,
   motte, muffled, mysterious, mystic, niche, nook, obfuscated,
   obscure, obscured, occult, occulted, packaged, pall, paved,
   plumage, port, possible, potential, privately, privy, quiet,
   recess, recondite, refuge, retreat, roofed-in, run, safety zone,
   sanctuary, screen, screened, scummed, secluded, secluse, secret,
   secret place, sequestered, sheathed, shelled, shelter, shield,
   shielded, shifty, shroud, shrouded, skulking, sleeping, slinking,
   slinky, sly, sneaking, sneaky, speculum, stash, stealthily,
   stealthy, storm cave, storm cellar, sub rosa, submerged,
   surreptitious, surreptitiously, swathed, tented, thicket, thickset,
   trench, tunnel, under an eclipse, under cover, under house arrest,
   under the surface, under wraps, under-the-counter, under-the-table,
   undercover, undercovert, underground, underhand, underhanded,
   underlying, unknown, unmanifested, unobtrusive, veil, veiled,
   vestment, virtual, walled, walled-in, wrapped, wrapped in clouds



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

COVERT, BARON. A wife; so called, from her being under the cover or
protection of her husband, baron or lord.