Source : Webster's Revised Unabridged Dictionary (1913)

Hour \Hour\, n. [OE. hour, our, hore, ure, OF. hore, ore, ure,
   F. heure, L. hora, fr. Gr. ?, orig., a definite space of
   time, fixed by natural laws; hence, a season, the time of the
   day, an hour. See {Year}, and cf. {Horologe}, {Horoscope}.]
   1. The twenty-fourth part of a day; sixty minutes.

   2. The time of the day, as expressed in hours and minutes,
      and indicated by a timepiece; as, what is the hour? At
      what hour shall we meet?

   3. Fixed or appointed time; conjuncture; a particular time or
      occasion; as, the hour of greatest peril; the man for the
      hour.

            Woman, . . . mine hour is not yet come. --John ii.
                                                  4.

            This is your hour, and the power of darkness. --Luke
                                                  xxii. 53.

   4. pl. (R. C. Ch.) Certain prayers to be repeated at stated
      times of the day, as matins and vespers.

   5. A measure of distance traveled.

            Vilvoorden, three hours from Brussels. --J. P.
                                                  Peters.

   {After hours}, after the time appointed for one's regular
      labor.

   {Canonical hours}. See under {Canonical}.

   {Hour angle} (Astron.), the angle between the hour circle
      passing through a given body, and the meridian of a place.
      

   {Hour circle}. (Astron.)
      (a) Any circle of the sphere passing through the two poles
          of the equator; esp., one of the circles drawn on an
          artificial globe through the poles, and dividing the
          equator into spaces of 15[deg], or one hour, each.
      (b) A circle upon an equatorial telescope lying parallel
          to the plane of the earth's equator, and graduated in
          hours and subdivisions of hours of right ascension.
      (c) A small brass circle attached to the north pole of an
          artificial globe, and divided into twenty-four parts
          or hours. It is used to mark differences of time in
          working problems on the globe.

   {Hour hand}, the hand or index which shows the hour on a
      timepiece.

   {Hour line}.
      (a) (Astron.) A line indicating the hour.
      (b) (Dialing) A line on which the shadow falls at a given
          hour; the intersection of an hour circle which the
          face of the dial.

   {Hour plate}, the plate of a timepiece on which the hours are
      marked; the dial. --Locke.

   {Sidereal hour}, the twenty-fourth part of a sidereal day.

   {Solar hour}, the twenty-fourth part of a solar day.

   {The small hours}, the early hours of the morning, as one
      o'clock, two o'clock, etc.

Source : WordNet®

hour circle
     n : a great circle on the celestial sphere that passes through
         both celestial poles