The Collaborative International Dictionary of English v.0.48:

Secure \Se*cure"\, v. t. [imp. & p. p. Secured; p. pr. & vb.
   n. Securing.]
   1. To make safe; to relieve from apprehensions of, or
      exposure to, danger; to guard; to protect.
      [1913 Webster]

            I spread a cloud before the victor's sight,
            Sustained the vanquished, and secured his flight.
                                                  --Dryden.
      [1913 Webster]

   2. To put beyond hazard of losing or of not receiving; to
      make certain; to assure; to insure; -- frequently with
      against or from, rarely with of; as, to secure a creditor
      against loss; to secure a debt by a mortgage.
      [1913 Webster]

            It secures its possessor of eternal happiness. --T.
                                                  Dick.
      [1913 Webster]

   3. To make fast; to close or confine effectually; to render
      incapable of getting loose or escaping; as, to secure a
      prisoner; to secure a door, or the hatches of a ship.
      [1913 Webster]

   4. To get possession of; to make one's self secure of; to
      acquire certainly; as, to secure an estate.
      [1913 Webster]

   Secure arms (Mil.), a command and a position in the manual
      of arms, used in wet weather, the object being to guard
      the firearm from becoming wet. The piece is turned with
      the barrel to the front and grasped by the right hand at
      the lower band, the muzzle is dropped to the front, and
      the piece held with the guard under the right arm, the
      hand supported against the hip, and the thumb on the
      rammer.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Secure \Se*cure"\, a. [L. securus; pref. se- without + cura
   care. See Cure care, and cf. Sure, a.]
   1. Free from fear, care, or anxiety; easy in mind; not
      feeling suspicion or distrust; confident.
      [1913 Webster]

            But thou, secure of soul, unbent with woes.
                                                  --Dryden.
      [1913 Webster]

   2. Overconfident; incautious; careless; -- in a bad sense.
      --Macaulay.
      [1913 Webster]

   3. Confident in opinion; not entertaining, or not having
      reason to entertain, doubt; certain; sure; -- commonly
      with of; as, secure of a welcome.
      [1913 Webster]

            Confidence then bore thee on, secure
            Either to meet no danger, or to find
            Matter of glorious trial.             --Milton.
      [1913 Webster]

   4. Not exposed to danger; safe; -- applied to persons and
      things, and followed by against or from. "Secure from
      fortune's blows." --Dryden.
      [1913 Webster]

   Syn: Safe; undisturbed; easy; sure; certain; assured;
        confident; careless; heedless; inattentive.
        [1913 Webster]

WordNet (r) 3.0 (2006):

secure
    adj 1: free from fear or doubt; easy in mind; "he was secure
           that nothing will be held against him" [syn: secure,
           unafraid, untroubled] [ant: insecure]
    2: free from danger or risk; "secure from harm"; "his fortune
       was secure"; "made a secure place for himself in his field"
       [ant: insecure, unsafe]
    3: not likely to fail or give way; "the lock was secure"; "a
       secure foundation"; "a secure hold on her wrist" [ant:
       insecure]
    4: immune to attack; incapable of being tampered with; "an
       impregnable fortress"; "fortifications that made the frontier
       inviolable"; "a secure telephone connection" [syn:
       impregnable, inviolable, secure, strong,
       unassailable, unattackable]
    5: financially sound; "a good investment"; "a secure investment"
       [syn: dependable, good, safe, secure]
    v 1: get by special effort; "He procured extra cigarettes even
         though they were rationed" [syn: procure, secure]
    2: cause to be firmly attached; "fasten the lock onto the door";
       "she fixed her gaze on the man" [syn: fasten, fix,
       secure] [ant: unfasten]
    3: assure payment of
    4: make certain of; "This nest egg will ensure a nice retirement
       for us"; "Preparation will guarantee success!" [syn:
       guarantee, ensure, insure, assure, secure]
    5: fill or close tightly with or as if with a plug; "plug the
       hole"; "stop up the leak" [syn: plug, stop up, secure]
    6: furnish with battens; "batten ships" [syn: batten, batten
       down, secure]

Moby Thesaurus II by Grady Ward, 1.0:

392 Moby Thesaurus words for "secure":
   accept, acquire, admit, advocate, affix, anchor, anchored, annex,
   arm, armor, arouse, arrogant, arrogate, ascertained, assume,
   assumed, assure, assured, attach, attest, attested, back, bag,
   balanced, bang, bar, barricade, batten, batten down, be seized of,
   be sponsor for, belay, believing, bind, bless, bolt, bond, bonded,
   bridle, bring, bring back, bring forth, bring out, bring to light,
   bulwark, button, button up, calculable, call a strike, call for,
   call forth, call it quits, call out, call up, capture, catch,
   cement, cemented, certain, certified, certify, chain, champion,
   chase after, choke, choke off, cinch, clamp, clap, clinch, cloak,
   close, close down, close shop, close up, closed, cocksure, collar,
   come by, come in for, come into, compass about, confident, confirm,
   constrict, contain, contract, convinced, cool, copyright, corral,
   cosy, countersecure, cover, cramp, cushion, decided, deduce,
   defend, definite, dependable, derive, derive from, determinate,
   determined, devout, dogmatic, doubtless, drag down, drag out, draw,
   draw forth, draw from, draw out, earn, easy, educe, elicit,
   enchain, endorse, engraft, ensure, ensured, enter into possession,
   entrammel, established, evident, evoke, faithful, faithworthy,
   fast, fasten, fasten down, fastened, fence, fend, fetch,
   fetch and carry, fetter, fideistic, fiducial, firm,
   firm as Gibraltar, fix, fixed, flank, fold, fold up, gain, get,
   get from, get hold of, get out of, glued, go after, go and get,
   go fetch, go for, go get, go on strike, go to get, good, graft,
   grapple, guarantee, guaranteed, guaranty, guard, guard against,
   gyve, hamper, handcuff, harbor, harvest, have, have coming in,
   haven, healthy, hobble, hog-tie, hopple, hubristic, hypothecate,
   immovable, immune, immunized, imperturbable, impressed with,
   in equilibrium, in the bag, induce, inevitable, insure, insured,
   intact, invincible, jammed, keep, keep from harm, key, knit,
   knock off, lash, latch, lay off, leash, lock, lock out, lock up,
   locked up, made sure, make, make fast, make safe, make secure,
   make sure, manacle, moor, moored, nail, nailed down, nestle, net,
   obtain, obvious, occlude, on ice, open-and-shut, overconfident,
   oversure, overweening, padlock, patent, peg down, persuaded,
   pick up, picket, pietistic, pin down, pinion, pious, pistic, plumb,
   poised, police, pompous, positive, predictable, prehend, preserve,
   probable, procure, produce, profitable, protect, protected, proud,
   proved, pull down, put in irons, put to, reap, reassured, receive,
   register, reliable, restrain, retrieve, ride shotgun for, rivet,
   rope, rouse, run after, sack, safe, safe and sound, safeguard,
   sanguine, satisfied, score, screen, screw up, seal, seal off,
   seal up, self, self-assured, self-confident, self-important,
   self-reliant, set, set to, settled, shackle, shag, shelter,
   sheltered, shield, shielded, shroud, shut, shut down,
   shut the door, shut up, shut up shop, sign, sign for, slam, snap,
   snug, sold on, solid, sound, sponsor, squeeze shut, stable,
   stand behind, stand up for, stated, staunch, steadfast, steady,
   stimulate, straitjacket, strangle, strap, strike, strong, stuck,
   sturdy, subscribe to, substantial, summon forth, summon up, sure,
   surefire, take, take in, take on, take over, take possession of,
   taped, tested, tether, tie, tie down, tie up, tight, tighten,
   trammel, trice up, tried, trim, trustworthy, trusty, unafraid,
   undamaged, under the impression, undersign, underwrite, undoubtful,
   undoubting, unexposed, unfailing, unfaltering, unflappable,
   unflinching, unharmed, unhesitating, unhurt, unquestionable,
   unscathed, unshakable, unthreatened, untouched, unwavering,
   walk out, wangle, wangle out of, warrant, warranted, wedged,
   well-balanced, well-founded, well-grounded, win, winkle out,
   without nerves, worm out, worm out of, zip up, zipper