The Collaborative International Dictionary of English v.0.48:

Stage \Stage\ (st[=a]j), n. [OF. estage, F. ['e]tage, (assumed)
   LL. staticum, from L. stare to stand. See Stand, and cf.
   Static.]
   1. A floor or story of a house. [Obs.] --Wyclif.
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   2. An elevated platform on which an orator may speak, a play
      be performed, an exhibition be presented, or the like.
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   3. A floor elevated for the convenience of mechanical work,
      or the like; a scaffold; a staging.
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   4. A platform, often floating, serving as a kind of wharf.
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   5. The floor for scenic performances; hence, the theater; the
      playhouse; hence, also, the profession of representing
      dramatic compositions; the drama, as acted or exhibited.
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            Knights, squires, and steeds, must enter on the
            stage.                                --Pope.
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            Lo! where the stage, the poor, degraded stage,
            Holds its warped mirror to a gaping age. --C.
                                                  Sprague.
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   6. A place where anything is publicly exhibited; the scene of
      any noted action or career; the spot where any remarkable
      affair occurs; as, politicians must live their lives on
      the public stage.
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            When we are born, we cry that we are come
            To this great stage of fools.         --Shak.
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            Music and ethereal mirth
            Wherewith the stage of air and earth did ring.
                                                  --Miton.
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   7. The platform of a microscope, upon which an object is
      placed to be viewed. See Illust. of Microscope.
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   8. A place of rest on a regularly traveled road; a stage
      house; a station; a place appointed for a relay of horses.
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   9. A degree of advancement in a journey; one of several
      portions into which a road or course is marked off; the
      distance between two places of rest on a road; as, a stage
      of ten miles.
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            A stage . . . signifies a certain distance on a
            road.                                 --Jeffrey.
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            He traveled by gig, with his wife, his favorite
            horse performing the journey by easy stages.
                                                  --Smiles.
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   10. A degree of advancement in any pursuit, or of progress
       toward an end or result.
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             Such a polity is suited only to a particular stage
             in the progress of society.          --Macaulay.
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   11. A large vehicle running from station to station for the
       accommodation of the public; a stagecoach; an omnibus. "A
       parcel sent you by the stage." --Cowper. [Obsolescent]
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             I went in the sixpenny stage.        --Swift.
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   12. (Biol.) One of several marked phases or periods in the
       development and growth of many animals and plants; as,
       the larval stage; pupa stage; zoea stage.
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   Stage box, a box close to the stage in a theater.

   Stage carriage, a stagecoach.

   Stage door, the actors' and workmen's entrance to a
      theater.

   Stage lights, the lights by which the stage in a theater is
      illuminated.

   Stage micrometer, a graduated device applied to the stage
      of a microscope for measuring the size of an object.

   Stage wagon, a wagon which runs between two places for
      conveying passengers or goods.

   Stage whisper, a loud whisper, as by an actor in a theater,
      supposed, for dramatic effect, to be unheard by one or
      more of his fellow actors, yet audible to the audience; an
      aside.
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WordNet (r) 3.0 (2006):

stage door
    n 1: an entrance to the backstage area of theater; used by
         performers and other theater personnel