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.
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            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]