Arch (?), n. [F. arche, fr. LL. arca, for arcus. See Arc.] 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.

☞ 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." Milton.

Triumphal arch, a monumental structure resembling an arched gateway, with one or more passages, erected to commemorate a triumph.

Arch (ärch), a. [See Arch-, pref.] 1. Chief; eminent; greatest; principal.

The most arch act of piteous massacre.

2. Cunning or sly; sportively mischievous; roguish; as, an arch look, word, lad.

[He] spoke his request with so arch a leer.

Arch, n. [See Arch-, pref.] A chief. [Obs.]

My worthy arch and patron comes to-night.

Arch, v. t. [imp. & p. p. Arched (?); p. pr. & vb. n. Arching.] 1. To cover with an arch or arches.

2. To form or bend into the shape of an arch.

The horse arched his neck.

Arch, v. i. To form into an arch; to curve.