The Collaborative International Dictionary of English v.0.48:

Gap \Gap\ (g[a^]p), n. [OE. gap; cf. Icel. gap an empty space,
   Sw. gap mouth, breach, abyss, Dan. gab mouth, opening, AS.
   geap expanse; as adj., wide, spacious. See Gape.]
   1. An opening in anything made by breaking or parting; as, a
      gap in a fence; an opening for a passage or entrance; an
      opening which implies a breach or defect; a vacant space
      or time; a hiatus; a mountain pass.
      [1913 Webster]

            Miseries ensued by the opening of that gap.
                                                  --Knolles.
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            It would make a great gap in your own honor. --Shak.
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   2. (A["e]ronautics) The vertical distance between two
      superposed surfaces, esp. in a biplane.
      [Webster 1913 Suppl.]

   Gap lathe (Mach.), a turning lathe with a deep notch in the
      bed to admit of turning a short object of large diameter.


   To stand in the gap, to expose one's self for the
      protection of something; to make defense against any
      assailing danger; to take the place of a fallen defender
      or supporter.

   To stop a gap, to secure a weak point; to repair a defect.
      [1913 Webster]