Webster's Revised Unabridged Dictionary · 1913

Gap

Gap (gap) , noun

[Old English gap; compare Icelandic gap an empty space, Swedish gap mouth, breach, abyss, Danish gab mouth, opening, Anglo-Saxon 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.
Miseries ensued by the opening of that gap. — Knolles
It would make a great gap in your own honor. — Shakespeare
2.
(Aeronautics) The vertical distance between two superposed surfaces, esp. in a biplane.
Collocations (3)
Gap lathe (Machinery) , 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.

Gap , transitive verb

1.
To notch, as a sword or knife.
2.
To make an opening in; to breach.
Their masses are gapp'd with our grape. — Tennyson