: an anatomical structure that resembles an arch in form or function: as a: either of two vaulted portions of the bony structure of the foot that impart elasticity to it: (1): a longitudinal arch supported posteriorly by the basal tuberosity of the calcaneus and anteriorly by the heads of the metatarsal bones (2): a transverse arch consisting of the metatarsals and first row of tarsals and resulting from elevation of the central anterior portion of the median longitudinal arch b:arch of the aorta
: a fingerprint in which all the ridges run from side to side and make no backward turn
Curved structure that spans the opening between two piers or columns and supports loads from above. The masonry arch provides the stepping stone from the post-and-beam system to the evolution of the vault, and was first widely used by the Romans. Its construction depends on a series of wedge-shaped blocks (voussoirs) set side by side in a semicircular curve or along two intersecting arcs (as in a pointed arch). The central voussoir is called the keystone, and the two points where the arch rests on its supports are known as the spring points. An arch can carry a much greater load than a horizontal beam of the same size and material, because downward pressure forces the voussoirs together instead of apart. The resulting outward thrust must be resisted by the arch's supports. Present-day lightweight monolithic (one-piece) arches of steel, concrete, or laminated wood are highly rigid, and thereby minimize horizontal thrust.