Source : Webster's Revised Unabridged Dictionary (1913)

Arch \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.

   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.'' --Milton.

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

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

         My worthy arch and patron comes to-night. --Shak.

Arch \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.            --Charlesworth.

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

Arch \Arch\ (["a]rch), a. [See {Arch-}, pref.]
   1. Chief; eminent; greatest; principal.

            The most arch act of piteous massacre. --Shak.

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

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

Source : WordNet®

arch
     adj 1: (of persons) highest in rank or authority or office; "his
            arch rival" [syn: {arch(a)}]
     2: (used of behavior or attitude) characteristic of those who
        treat others with condescension [syn: {condescending}, {patronizing},
         {patronising}]
     3: expert in skulduggery; "an arch criminal" [syn: {arch(a)}]

arch
     n 1: a curved shape in the vertical plane that spans an opening
     2: a curved bony structure supporting or enclosing organs
        (especially arches of the feet)
     3: a passageway under an arch [syn: {archway}]
     4: (architecture) a masonry construction (usually curved) for
        spanning an opening and supporting the weight above it

arch
     v : form an arch or curve; "her back arches"; "her hips curve
         nicely" [syn: {curve}, {arc}]