a. [ See Arch-, pref. ] 1. Chief; eminent; greatest; principal. [ 1913 Webster ]

The most arch act of piteous massacre. Shak. [ 1913 Webster ]

2. Cunning or sly; sportively mischievous; roguish; as, an arch look, word, lad. [ 1913 Webster ]

[ He ] spoke his request with so arch a leer. Tatler. [ 1913 Webster ]

n. [ F. arche, fr. LL. arca, for arcus. See Arc. ] 1. (Geom.) Any part of a curved line. [ 1913 Webster ]

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. [ 1913 Webster ]

☞ Scientifically considered, the arch is a means of spanning an opening by resolving vertical pressure into horizontal or diagonal thrust. [ 1913 Webster ]

3. Any place covered by an arch; an archway; as, to pass into the arch of a bridge. [ 1913 Webster ]

4. Any curvature in the form of an arch; as, the arch of the aorta. “Colors of the showery arch.” Milton. [ 1913 Webster ]

Triumphal arch, a monumental structure resembling an arched gateway, with one or more passages, erected to commemorate a triumph. [ 1913 Webster ]

v. t. [ imp. & p. p. Arched p. pr. & vb. n. Arching. ] 1. To cover with an arch or arches. [ 1913 Webster ]

2. To form or bend into the shape of an arch. [ 1913 Webster ]

The horse arched his neck. Charlesworth. [ 1913 Webster ]

n. [ See Arch-, pref. ] A chief. [ Obs. ] [ 1913 Webster ]

My worthy arch and patron comes to-night. Shak. [ 1913 Webster ]

v. i. To form into an arch; to curve. [ 1913 Webster ]

[ L. arch-, Gr. 'arch- = 'archi-. See Arch-. ] A prefix signifying chief, as in archbuilder, archfiend. [ 1913 Webster ]

n. (Geol.) The earliest period in geological period, extending up to the Lower Silurian. It includes an Azoic age, previous to the appearance of life, and an Eozoic age, including the earliest forms of life. [ 1913 Webster ]

☞ This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson. [ 1913 Webster ]

a. [ Gr. 'archai^os ancient, fr. 'archh` beginning. ] Ancient; pertaining to the earliest period in geological history. [ 1913 Webster ]

, n. (Microbiol.) A group of single-celled microorganisms including the methanogens and some halophiles and thermoacidophiles, recognized in the 1970's by C. R. Woese and his colleagues as being a distinct group on the basis of RNA sequences, cell walls, and coenzymes differing from those of other microbes. It is believed to be an ancient form of living organism that evolved separately from the eubacteria and blue-green algae. It is classified as a separate kingdom by some taxonomists. See also The Archaebacteria. [ PJC ]

n. [ Gr. 'archai^os ancient + -graphy. ] A description of, or a treatise on, antiquity or antiquities. [ 1913 Webster ]