The Collaborative International Dictionary of English v.0.48:

Portal \Por"tal\, n. [OF. portal, F. portail, LL. portale, fr.
   L. porta a gate. See Port a gate.]
   1. A door or gate; hence, a way of entrance or exit,
      especially one that is grand and imposing.
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            Thick with sparkling orient gems
            The portal shone.                     --Milton.
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            From out the fiery portal of the east. --Shak.
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   2. (Arch.)
      (a) The lesser gate, where there are two of different
          dimensions.
      (b) Formerly, a small square corner in a room separated
          from the rest of the apartment by wainscoting, forming
          a short passage to another apartment.
      (c) By analogy with the French portail, used by recent
          writers for the whole architectural composition which
          surrounds and includes the doorways and porches of a
          church.
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   3. (Bridge Building) The space, at one end, between opposite
      trusses when these are terminated by inclined braces.
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   4. A prayer book or breviary; a portass. [Obs.]
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   Portal bracing (Bridge Building), a combination of struts
      and ties which lie in the plane of the inclined braces at
      a portal, serving to transfer wind pressure from the upper
      parts of the trusses to an abutment or pier of the bridge.
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