Gap

A rent or opening in a wall (Ezekiel 13:5; Compare Amos 4:3). The false prophets did not stand in the gap (Ezekiel 22:: 30), i.e., they did nothing to stop the outbreak of wickedness.

Source: Easton's Bible Dictionary
Gap

GAP, n. See Gape and Gab.

1. An opening in any thing made by breaking or parting; as a gap in a fence or wall.
2. A breach.

Manifold miseries ensued by the opening of that gap to all that side of christendom.

3. Any avenue or passage; way of entrance or departure.
4. A breach; a defect; a flaw; as a gap in honor or reputation.
5. An interstice; a vacuity.

A third can fill the gap with laughing.

6. A hiatus; a chasm; as a gap between words.

To stop a gap, to secure a weak point; to repair a defect.

To stand in the gap, to expose one's self for the protection of something; to make defense against any assailing danger. Ezek. 22.

Source: King James Dictionary