The Collaborative International Dictionary of English v.0.48:

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.
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   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?
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   3. Fixed or appointed time; conjuncture; a particular time or
      occasion; as, the hour of greatest peril; the man for the
      hour.
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            Woman, . . . mine hour is not yet come. --John ii.
                                                  4.
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            This is your hour, and the power of darkness. --Luke
                                                  xxii. 53.
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   4. pl. (R. C. Ch.) Certain prayers to be repeated at stated
      times of the day, as matins and vespers.
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   5. A measure of distance traveled.
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            Vilvoorden, three hours from Brussels. --J. P.
                                                  Peters.
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   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.

   To keep good hours, to be regular in going to bed early.
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WordNet (r) 3.0 (2006):

hour angle
    n 1: the angular distance along the celestial equator from the
         observer's meridian to the hour circle of a given celestial
         body
    2: (astronomy) the angular distance of a celestial point
       measured westward along the celestial equator from the zenith
       crossing; the right ascension for an observer at a particular
       location and time of day [syn: hour angle, HA]