Source : Webster's Revised Unabridged Dictionary (1913)

Vertical \Ver"ti*cal\, a. [Cf. F. vertical. See {Vertex}.]
   1. Of or pertaining to the vertex; situated at the vertex, or
      highest point; directly overhead, or in the zenith;
      perpendicularly above one.

            Charity . . . is the vertical top of all religion.
                                                  --Jer. Taylor.

   2. Perpendicular to the plane of the horizon; upright; plumb;
      as, a vertical line.

   {Vertical angle} (Astron. & Geod.), an angle measured on a
      vertical circle, called an angle of elevation, or
      altitude, when reckoned from the horizon upward, and of
      depression when downward below the horizon.

   {Vertical anthers} (Bot.), such anthers as stand erect at the
      top of the filaments.

   {Vertical circle} (Astron.), an azimuth circle. See under
      {Azimuth}.

   {Vertical drill}, an drill. See under {Upright}.

   {Vertical fire} (Mil.), the fire, as of mortars, at high
      angles of elevation.

   {Vertical leaves} (Bot.), leaves which present their edges to
      the earth and the sky, and their faces to the horizon, as
      in the Australian species of Eucalyptus.

   {Vertical limb}, a graduated arc attached to an instrument,
      as a theodolite, for measuring vertical angles.

   {Vertical line}.
      (a) (Dialing) A line perpendicular to the horizon.
      (b) (Conic Sections) A right line drawn on the vertical
          plane, and passing through the vertex of the cone.
      (c) (Surv.) The direction of a plumb line; a line normal
          to the surface of still water.
      (d) (Geom., Drawing, etc.) A line parallel to the sides of
          a page or sheet, in distinction from a horizontal line
          parallel to the top or bottom.

   {Vertical plane}.
      (a) (Conic Sections) A plane passing through the vertex of
          a cone, and through its axis.
      (b) (Projections) Any plane which passes through a
          vertical line.
      (c) (Persp.) The plane passing through the point of sight,
          and perpendicular to the ground plane, and also to the
          picture.

   {Vertical sash}, a sash sliding up and down. Cf. {French
      sash}, under 3d {Sash}.

   {Vertical steam engine}, a steam engine having the crank
      shaft vertically above or below a vertical cylinder.

Azimuth \Az"i*muth\, n. [OE. azimut, F. azimut, fr. Ar.
   as-sum?t, pl. of as-samt a way, or perh., a point of the
   horizon and a circle extending to it from the zenith, as
   being the Arabic article: cf. It. azzimutto, Pg. azimuth, and
   Ar. samt-al-r[=a]'s the vertex of the heaven. Cf. {Zenith}.]
   (Astron. & Geodesy)
      (a) The quadrant of an azimuth circle.
      (b) An arc of the horizon intercepted between the meridian
          of the place and a vertical circle passing through the
          center of any object; as, the azimuth of a star; the
          azimuth or bearing of a line surveying.

   Note: In trigonometrical surveying, it is customary to reckon
         the azimuth of a line from the south point of the
         horizon around by the west from 0[deg] to 360[deg].

   {Azimuth circle}, or {Vertical circle}, one of the great
      circles of the sphere intersecting each other in the
      zenith and nadir, and cutting the horizon at right angles.
      --Hutton.

   {Azimuth compass}, a compass resembling the mariner's
      compass, but having the card divided into degrees instead
      of rhumbs, and having vertical sights; used for taking the
      magnetic azimuth of a heavenly body, in order to find, by
      comparison with the true azimuth, the variation of the
      needle.

   {Azimuth dial}, a dial whose stile or gnomon is at right
      angles to the plane of the horizon. --Hutton.

   {Magnetic azimuth}, an arc of the horizon, intercepted
      between the vertical circle passing through any object and
      the magnetic meridian. This is found by observing the
      object with an azimuth compass.

Circle \Cir"cle\ (s[~e]r"k'l), n. [OE. cercle, F. cercle, fr. L.
   circulus (Whence also AS. circul), dim. of circus circle,
   akin to Gr. kri`kos, ki`rkos, circle, ring. Cf. {Circus},
   {Circum-}.]
   1. A plane figure, bounded by a single curve line called its
      circumference, every part of which is equally distant from
      a point within it, called the center.

   2. The line that bounds such a figure; a circumference; a
      ring.

   3. (Astron.) An instrument of observation, the graduated limb
      of which consists of an entire circle.

   Note: When it is fixed to a wall in an observatory, it is
         called a {mural circle}; when mounted with a telescope
         on an axis and in Y's, in the plane of the meridian, a
         {meridian or transit circle}; when involving the
         principle of reflection, like the sextant, a
         {reflecting circle}; and when that of repeating an
         angle several times continuously along the graduated
         limb, a {repeating circle}.

   4. A round body; a sphere; an orb.

            It is he that sitteth upon the circle of the earth.
                                                  --Is. xi. 22.

   5. Compass; circuit; inclosure.

            In the circle of this forest.         --Shak.

   6. A company assembled, or conceived to assemble, about a
      central point of interest, or bound by a common tie; a
      class or division of society; a coterie; a set.

            As his name gradually became known, the circle of
            his acquaintance widened.             --Macaulay.

   7. A circular group of persons; a ring.

   8. A series ending where it begins, and repeating itself.

            Thus in a circle runs the peasant's pain. --Dryden.

   9. (Logic) A form of argument in which two or more unproved
      statements are used to prove each other; inconclusive
      reasoning.

            That heavy bodies descend by gravity; and, again,
            that gravity is a quality whereby a heavy body
            descends, is an impertinent circle and teaches
            nothing.                              --Glanvill.

   10. Indirect form of words; circumlocution. [R.]

             Has he given the lie, In circle, or oblique, or
             semicircle.                          --J. Fletcher.

   11. A territorial division or district.

   Note:

   {The Circles of the Holy Roman Empire}, ten in number, were
      those principalities or provinces which had seats in the
      German Diet.

   {Azimuth circle}. See under {Azimuth}.

   {Circle of altitude} (Astron.), a circle parallel to the
      horizon, having its pole in the zenith; an almucantar.

   {Circle of curvature}. See {Osculating circle of a curve}
      (Below).

   {Circle of declination}. See under {Declination}.

   {Circle of latitude}.
       (a) (Astron.) A great circle perpendicular to the plane
           of the ecliptic, passing through its poles.
       (b) (Spherical Projection) A small circle of the sphere
           whose plane is perpendicular to the axis.

   {Circles of longitude}, lesser circles parallel to the
      ecliptic, diminishing as they recede from it.

   {Circle of perpetual apparition}, at any given place, the
      boundary of that space around the elevated pole, within
      which the stars never set. Its distance from the pole is
      equal to the latitude of the place.

   {Circle of perpetual occultation}, at any given place, the
      boundary of the space around the depressed pole, within
      which the stars never rise.

   {Circle of the sphere}, a circle upon the surface of the
      sphere, called a great circle when its plane passes
      through the center of the sphere; in all other cases, a
      small circle.

   {Diurnal circle}. See under {Diurnal}.

   {Dress circle}, a gallery in a theater, generally the one
      containing the prominent and more expensive seats.

   {Druidical circles} (Eng. Antiq.), a popular name for certain
      ancient inclosures formed by rude stones circularly
      arranged, as at Stonehenge, near Salisbury.

   {Family circle}, a gallery in a theater, usually one
      containing inexpensive seats.

   {Horary circles} (Dialing), the lines on dials which show the
      hours.

   {Osculating circle of a curve} (Geom.), the circle which
      touches the curve at some point in the curve, and close to
      the point more nearly coincides with the curve than any
      other circle. This circle is used as a measure of the
      curvature of the curve at the point, and hence is called
      circle of curvature.

   {Pitch circle}. See under {Pitch}.

   {Vertical circle}, an azimuth circle.

   {Voltaic} {circle or circuit}. See under {Circuit}.

   {To square the circle}. See under {Square}.

   Syn: Ring; circlet; compass; circuit; inclosure.

Source : WordNet®

vertical circle
     n : a great circle on the celestial sphere passing through the
         zenith and perpendicular to the horizon