The Collaborative International Dictionary of English v.0.48:

Open \O"pen\ v. t. [imp. & p. p. Opened; p. pr. & vb. n.
   Opening.] [AS. openian. See Open,a.]
   1. To make or set open; to render free of access; to unclose;
      to unbar; to unlock; to remove any fastening or covering
      from; as, to open a door; to open a box; to open a room;
      to open a letter.
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            And all the windows of my heart
            I open to the day.                    --Whittier.
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   2. To spread; to expand; as, to open the hand.
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   3. To disclose; to reveal; to interpret; to explain.
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            The king opened himself to some of his council, that
            he was sorry for the earl's death.    --Bacon.
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            Unto thee have I opened my cause.     --Jer. xx. 12.
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            While he opened to us the Scriptures. --Luke xxiv.
                                                  32.
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   4. To make known; to discover; also, to render available or
      accessible for settlements, trade, etc.
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            The English did adventure far for to open the North
            parts of America.                     --Abp. Abbot.
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   5. To enter upon; to begin; as, to open a discussion; to open
      fire upon an enemy; to open trade, or correspondence; to
      open an investigation; to open a case in court, or a
      meeting.
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   6. To loosen or make less compact; as, to open matted cotton
      by separating the fibers.
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   To open one's mouth, to speak.

   To open up, to lay open; to discover; to disclose.
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            Poetry that had opened up so many delightful views
            into the character and condition of our "bold
            peasantry, their country's pride."    --Prof.
                                                  Wilson.
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The Collaborative International Dictionary of English v.0.48:

Opening \O"pen*ing\, n.
   1. The act or process of opening; a beginning; commencement;
      first appearance; as, the opening of a speech.
      [1913 Webster]

            The opening of your glory was like that of light.
                                                  --Dryden.
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   2. A place which is open; a breach; an aperture; a gap;
      cleft, or hole.
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            We saw him at the opening of his tent. --Shak.
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   3. Hence: An opportunity; as, an opening for business.
      [Colloq.] --Dickens.
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   4. Hence: A vacant place; a job which does not have a current
      occupant; as, they are now interviewing candidates for the
      two openings in the department.
      [PJC]

   5. A thinly wooded space, without undergrowth, in the midst
      of a forest; a clearing; as, oak openings. [U.S.]
      --Cooper.
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WordNet (r) 3.0 (2006):

opening
    adj 1: first or beginning; "the memorable opening bars of
           Beethoven's Fifth"; "the play's opening scene" [ant:
           closing]
    n 1: an open or empty space in or between things; "there was a
         small opening between the trees"; "the explosion made a gap
         in the wall" [syn: opening, gap]
    2: a ceremony accompanying the start of some enterprise
    3: becoming open or being made open; "the opening of his arms
       was the sign I was waiting for"
    4: the first performance (as of a theatrical production); "the
       opening received good critical reviews" [syn: opening,
       opening night, curtain raising]
    5: the act of opening something; "the ray of light revealed his
       cautious opening of the door" [ant: closing, shutting]
    6: opportunity especially for employment or promotion; "there is
       an opening in the sales department"
    7: the initial part of the introduction; "the opening
       established the basic theme"
    8: a possible alternative; "bankruptcy is always a possibility"
       [syn: possibility, possible action, opening]
    9: an aperture or hole that opens into a bodily cavity; "the
       orifice into the aorta from the lower left chamber of the
       heart" [syn: orifice, opening, porta]
    10: a vacant or unobstructed space that is man-made; "they left
        a small opening for the cat at the bottom of the door"
    11: an entrance equipped with a hatch; especially a passageway
        between decks of a ship [syn: hatchway, opening,
        scuttle]
    12: a recognized sequence of moves at the beginning of a game of
        chess; "he memorized all the important chess openings" [syn:
        opening, chess opening]
    13: the first of a series of actions [syn: first step,
        initiative, opening move, opening]

Moby Thesaurus II by Grady Ward, 1.0:

296 Moby Thesaurus words for "opening":
   a leg up, abysm, abyss, access, adit, air lock, aisle, alley,
   alpha, ambulatory, aperture, apparition, appearance, appearing,
   appointment, approach, arcade, arising, arroyo, artery, avatar,
   avenue, bareness, barrenness, beginning, berth, billet, birth,
   blankness, blast-off, bleakness, blowhole, box canyon, breach,
   break, canyon, cavity, chance, channel, chap, chasm, check,
   chimney, chink, chute, clear stage, cleft, cleuch, cloister,
   clough, col, colonnade, coming, coming into being, coming-forth,
   commencement, communication, conduit, connection, corridor, coulee,
   couloir, covered way, crack, cranny, creation, crevasse, crevice,
   cut, cutting edge, cwm, dawn, dawning, debouch, debut, defile,
   dell, demonstration, desertedness, desolateness, dike, disclosure,
   discontinuity, display, ditch, donga, door, draw, edge, egress,
   emergence, employment, emptiness, emunctory, enactment, engagement,
   entrance, entranceway, entree, entry, entryway, epiphany, escape,
   establishment, estuary, excavation, exhaust, exhibit, exhibition,
   exit, exposition, exposure, fair field, fair game, fault, ferry,
   fissure, flaw, floodgate, flume, flying start, foothold, ford,
   forthcoming, foundation, fracture, fresh start, furrow, gallery,
   gangplank, gangway, gap, gape, gash, gig, gorge, groove, gulch,
   gulf, gully, hall, hole, hollowness, in, inanition, inauguration,
   incarnation, incision, incumbency, ingress, initiation, inlet,
   institution, intake, interchange, intersection, issuance, job,
   joint, jump-off, junction, kick-off, kloof, lane, launch,
   leading edge, leak, liberty, look-in, loophole, manifestation,
   materialization, materializing, means of access, moat,
   moonlighting, new departure, noninhabitance, nonoccupance,
   nonoccupancy, nonresidence, notch, nullah, occasion, occurrence,
   office, oncoming, onset, open arms, open door, opportunism,
   opportunity, orifice, origin, origination, ostentation, out,
   outbreak, outcome, outfall, outgate, outgo, outlet, outset,
   outstart, overpass, pass, passage, passageway, performance, pit,
   place, place open, pore, port, portico, position, post,
   presentation, presentment, production, projection, railroad tunnel,
   ravine, realization, rent, representation, retrospective,
   revelation, rift, rime, rise, rising, room, running start, rupture,
   sally port, scissure, scope, seam, second job, send-off,
   separation, service, setout, setting in motion, setting-up, shot,
   show, showing, showing forth, situation, slit, slot, sluice,
   spiracle, split, spout, square one, squeak, start, start-off,
   starting point, station, stepping-stone, take-off, tap, tenure,
   theophany, time, traject, trajet, trench, tunnel, underpass,
   unfolding, unfoldment, unveiling, vacancy, vacant post, vacuity,
   valley, varnishing day, vent, ventage, venthole, vernissage,
   vestibule, void, voidness, vomitory, wadi, way, way in, way out,
   weir