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The Collaborative International Dictionary of English v.0.48:

Meridian \Me*rid"i*an\, n. [F. m['e]ridien. See Meridian, a.] [1913 Webster] 1. Midday; noon. [1913 Webster] 2. Hence: The highest point, as of success, prosperity, or the like; culmination. [1913 Webster] I have touched the highest point of all my greatness, And from that full meridian of my glory I haste now to my setting. --Shak. [1913 Webster] 3. (Astron.) A great circle of the sphere passing through the poles of the heavens and the zenith of a given place. It is crossed by the sun at midday. [1913 Webster] 4. (Geog.) A great circle on the surface of the earth, passing through the poles and any given place; also, the half of such a circle included between the poles. [1913 Webster] Note: The planes of the geographical and astronomical meridians coincide. Meridians, on a map or globe, are lines drawn at certain intervals due north and south, or in the direction of the poles. [1913 Webster] Calculated for the meridian of, or fitted to the meridian of, or adapted to the meridian of, suited to the local circumstances, capabilities, or special requirements of. [1913 Webster] All other knowledge merely serves the concerns of this life, and is fitted to the meridian thereof. --Sir M. Hale. [1913 Webster] First meridian or prime meridian, the meridian from which longitudes are reckoned. The meridian of Greenwich is the one commonly employed in calculations of longitude by geographers, and in actual practice, although in various countries other and different meridians, chiefly those which pass through the capitals of the countries, are occasionally used; as, in France, the meridian of Paris; in the United States, the meridian of Washington, etc. Guide meridian (Public Land Survey), a line, marked by monuments, running North and South through a section of country between other more carefully established meridians called principal meridians, used for reference in surveying. [U.S.] Magnetic meridian, a great circle, passing through the zenith and coinciding in direction with the magnetic needle, or a line on the earth's surface having the same direction. Meridian circle (Astron.), an instrument consisting of a telescope attached to a large graduated circle and so mounted that the telescope revolves like the transit instrument in a meridian plane. By it the right ascension and the declination of a star may be measured in a single observation. Meridian instrument (Astron.), any astronomical instrument having a telescope that rotates in a meridian plane. Meridian of a globe, or Brass meridian, a graduated circular ring of brass, in which the artificial globe is suspended and revolves. [1913 Webster]
The Collaborative International Dictionary of English v.0.48:

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-.] [1913 Webster] 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. [1913 Webster] 2. The line that bounds such a figure; a circumference; a ring. [1913 Webster] 3. (Astron.) An instrument of observation, the graduated limb of which consists of an entire circle. [1913 Webster] 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 circle 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. [1913 Webster] 4. A round body; a sphere; an orb. [1913 Webster] It is he that sitteth upon the circle of the earth. --Is. xi. 22. [1913 Webster] 5. Compass; circuit; inclosure. [1913 Webster] In the circle of this forest. --Shak. [1913 Webster] 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. [1913 Webster] As his name gradually became known, the circle of his acquaintance widened. --Macaulay. [1913 Webster] 7. A circular group of persons; a ring. [1913 Webster] 8. A series ending where it begins, and repeating itself. [1913 Webster] Thus in a circle runs the peasant's pain. --Dryden. [1913 Webster] 9. (Logic) A form of argument in which two or more unproved statements are used to prove each other; inconclusive reasoning. [1913 Webster] 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. [1913 Webster] 10. Indirect form of words; circumlocution. [R.] [1913 Webster] Has he given the lie, In circle, or oblique, or semicircle. --J. Fletcher. [1913 Webster] 11. A territorial division or district. [1913 Webster] Note: The Circles of the Holy Roman Empire, ten in number, were those principalities or provinces which had seats in the German Diet. [1913 Webster] 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 circuit or Voltaic circle. See under Circuit. To square the circle. See under Square. Syn: Ring; circlet; compass; circuit; inclosure. [1913 Webster]