The Collaborative International Dictionary of English v.0.48:

Achromatic \Ach`ro*mat"ic\, a. [Gr. 'achrw`matos colorless; 'a
   priv. + chrw^ma, chrw`matos, color: cf. F. achromatique.]
   1. (Opt.) Free from color; transmitting light without
      decomposing it into its primary colors.
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   2. (Biol.) Uncolored; not absorbing color from a fluid; --
      said of tissue.
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   Achromatic lens (Opt.), a lens composed usually of two
      separate lenses, a convex and concave, of substances
      having different refractive and dispersive powers, as
      crown and flint glass, with the curvatures so adjusted
      that the chromatic aberration produced by the one is
      corrected by other, and light emerges from the compound
      lens undecomposed.

   Achromatic prism. See Prism.

   Achromatic telescope, or microscope, one in which the
      chromatic aberration is corrected, usually by means of a
      compound or achromatic object glass, and which gives
      images free from extraneous color.
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The Collaborative International Dictionary of English v.0.48:

Telescope \Tel"e*scope\, n. [Gr. ? viewing afar, farseeing; ?
   far, far off + ? a watcher, akin to ? to view: cf. F.
   t['e]lescope. See Telegraph, and -scope.]
   An optical instrument used in viewing distant objects, as the
   heavenly bodies.
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   Note: A telescope assists the eye chiefly in two ways; first,
         by enlarging the visual angle under which a distant
         object is seen, and thus magnifying that object; and,
         secondly, by collecting, and conveying to the eye, a
         larger beam of light than would enter the naked organ,
         thus rendering objects distinct and visible which would
         otherwise be indistinct and or invisible. Its essential
         parts are the object glass, or concave mirror, which
         collects the beam of light, and forms an image of the
         object, and the eyeglass, which is a microscope, by
         which the image is magnified.
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   Achromatic telescope. See under Achromatic.

   Aplanatic telescope, a telescope having an aplanatic
      eyepiece.

   Astronomical telescope, a telescope which has a simple
      eyepiece so constructed or used as not to reverse the
      image formed by the object glass, and consequently
      exhibits objects inverted, which is not a hindrance in
      astronomical observations.

   Cassegrainian telescope, a reflecting telescope invented by
      Cassegrain, which differs from the Gregorian only in
      having the secondary speculum convex instead of concave,
      and placed nearer the large speculum. The Cassegrainian
      represents objects inverted; the Gregorian, in their
      natural position. The Melbourne telescope (see Illust.
      under Reflecting telescope, below) is a Cassegrainian
      telescope.

   Dialytic telescope. See under Dialytic.

   Equatorial telescope. See the Note under Equatorial.

   Galilean telescope, a refracting telescope in which the
      eyeglass is a concave instead of a convex lens, as in the
      common opera glass. This was the construction originally
      adopted by Galileo, the inventor of the instrument. It
      exhibits the objects erect, that is, in their natural
      positions.

   Gregorian telescope, a form of reflecting telescope. See
      under Gregorian.

   Herschelian telescope, a reflecting telescope of the form
      invented by Sir William Herschel, in which only one
      speculum is employed, by means of which an image of the
      object is formed near one side of the open end of the
      tube, and to this the eyeglass is applied directly.

   Newtonian telescope, a form of reflecting telescope. See
      under Newtonian.

   Photographic telescope, a telescope specially constructed
      to make photographs of the heavenly bodies.

   Prism telescope. See Teinoscope.

   Reflecting telescope, a telescope in which the image is
      formed by a speculum or mirror (or usually by two
      speculums, a large one at the lower end of the telescope,
      and the smaller one near the open end) instead of an
      object glass. See Gregorian, Cassegrainian, Herschelian,
      & Newtonian, telescopes, above.

   Refracting telescope, a telescope in which the image is
      formed by refraction through an object glass.

   Telescope carp (Zool.), the telescope fish.

   Telescope fish (Zool.), a monstrous variety of the goldfish
      having very protuberant eyes.

   Telescope fly (Zool.), any two-winged fly of the genus
      Diopsis, native of Africa and Asia. The telescope flies
      are remarkable for having the eyes raised on very long
      stalks.

   Telescope shell (Zool.), an elongated gastropod (Cerithium
      telescopium) having numerous flattened whorls.

   Telescope sight (Firearms), a slender telescope attached to
      the barrel, having cross wires in the eyepiece and used as
      a sight.

   Terrestrial telescope, a telescope whose eyepiece has one
      or two lenses more than the astronomical, for the purpose
      of inverting the image, and exhibiting objects erect.
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