The Collaborative International Dictionary of English v.0.48:

Gregorian \Gre*go"ri*an\, a. [NL. Gregorianus, fr. Gregorius
   Gregory, Gr. ?: cf. F. gr['e]gorien.]
   Pertaining to, or originated by, some person named Gregory,
   especially one of the popes of that name.
   [1913 Webster]

   Gregorian calendar, the calendar as reformed by Pope
      Gregory XIII. in 1582, including the method of adjusting
      the leap years so as to harmonize the civil year with the
      solar, and also the regulation of the time of Easter and
      the movable feasts by means of epochs. See Gregorian
      year (below).

   Gregorian chant (Mus.), plain song, or canto fermo, a kind
      of unisonous music, according to the eight celebrated
      church modes, as arranged and prescribed by Pope Gregory
      I. (called "the Great") in the 6th century.

   Gregorian modes, the musical scales ordained by Pope
      Gregory the Great, and named after the ancient Greek
      scales, as Dorian, Lydian, etc.

   Gregorian telescope (Opt.), a form of reflecting telescope,
      named from Prof. James Gregory, of Edinburgh, who
      perfected it in 1663. A small concave mirror in the axis
      of this telescope, having its focus coincident with that
      of the large reflector, transmits the light received from
      the latter back through a hole in its center to the
      eyepiece placed behind it.

   Gregorian year, the year as now reckoned according to the
      Gregorian calendar. Thus, every year, of the current
      reckoning, which is divisible by 4, except those divisible
      by 100 and not by 400, has 366 days; all other years have
      365 days. See Bissextile, and Note under Style, n., 7.
      [1913 Webster]

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.
   [1913 Webster]

   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.
         [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Gregorian telescope
    n 1: a reflecting telescope that has a paraboloidal primary
         mirror and a hyperboloidal secondary mirror; light is
         brought to a focus through an aperture in the center of the
         primary mirror [syn: Cassegrainian telescope, Gregorian
         telescope]