n. 1. In geometry, any part of the circumference of a circle or other curve; an arc. See arcn. In architecture, a structure built of separate and inelastic blocks, assembled on a curved line in such a way as to retain their position when the structure is supported extraneously only at its two extremities.n. Any place covered with an arch or a vault like an arch: as, to pass through the arch of a bridge.n. Any curvature in the form of an arch: as, the arch of the aorta; the arch of an eyebrow, of the foot, of the heavens, etc.n. In mining, a portion of a lode left standing, either as being too poor for profitable working or because it is needed to support the adjacent rock.n. The roofing of the fire-chamber of a furnace, as a reverberatory or a glass-furnace; hence, sometimes, the fire-chamber itself.To cover with a vault, or span with an arch.To throw into the shape of an arch or vault; curve: as, the horse arches his neck.To form an arch or arches: as, the sky arches overhead.n. A box or chest; in plural, archives.n. The ark of Noah.n. The ark of the covenant.Chief; principal; preëminent. See arch-.Cunning; sly; shrewd; waggish; mischievous for sport; roguish: now commonly used of facial expression: as, “so arch a leer,”n. A chief; a leader.n. Chief; principal: a prefix much used in composition with words both of native and of foreign origin. See arch.