- The upper or exterior curve of an arch.
- The upper or convex surface of an arch or of a vault.
- The outer curve of a voussoir. See <internalXref urlencoded="arch">arch</internalXref>, 2.
- In <em>mech.</em>, the locus of the lower ends of wires, of uniform weight per unit of length, hanging down from points on a cord which is perfectly flexible, inextensible, and without weight. When the wires are equally distant from one another and of equal length, the extrados is a parabola.
- The exterior curve of an arch; esp., the upper curved face of the whole body of voussoirs. See <xref urlencoded="intrados">intrados</xref>.
- The <xref>outer</xref> or <xref>upper</xref> <xref>curve</xref> of an <xref>arch</xref>.
- the exterior curve of an arch