Arch n.
 1. Geom. Any part of a curved line.
 2. Arch. (a) Usually a curved member made up of separate wedge-shaped solids, with the joints between them disposed in the direction of the radii of the curve; used to support the wall or other weight above an opening.  In this sense arches are segmental, round (i. e., semicircular), or pointed. (b) A flat arch is a member constructed of stones cut into wedges or other shapes so as to support each other without rising in a curve.
 Note: ☞ Scientifically considered, the arch is a means of spanning an opening by resolving vertical pressure into horizontal or diagonal thrust.
 3. Any place covered by an arch; an archway; as, to pass into the arch of a bridge.
 4. Any curvature in the form of an arch; as, the arch of the aorta.  “Colors of the showery arch.”
 Triumphal arch, a monumental structure resembling an arched gateway, with one or more passages, erected to commemorate a triumph.
 triumphal arch
      n : a monumental archway; usually they are built to commemorate
          some notable victory