buttress

Medieval builders had a problem that was both simple and terrifying: a heavy stone roof pushes outward on the walls, trying to make them burst like a box. Their solution was the buttress, a massive shoulder of masonry leaning against the building, and the word arrived through Old French ars bouterez, “supporting arcs.” The key verb meant “to push” or “to thrust,” and farther back it belongs to the reconstructed Proto-Indo-European root *bhau-, “to strike”—the same ancient family that gave English beat and butt. By the early 14th century, buttress named a physical prop; by the mid-15th century, people were using it for emotional, political, or intellectual support too. So when evidence buttresses an argument, the metaphor still pictures stone resisting a wall’s sideways shove.