flying buttress

This term refers to a specific architectural innovation of the Gothic period, designed to shift the weight of heavy stone vaults away from the walls. By transferring the lateral thrust to external piers, architects were able to build much taller walls and incorporate expansive stained-glass windows, which would have otherwise caused the structure to collapse.

In a technical sense, the term is used exclusively within the context of masonry and structural engineering. It is rarely used metaphorically, though when it is, it typically refers to an external support system that prevents a larger, precarious structure from failing.