An hour is a unit of time — it's sixty minutes, 3,600 seconds, or the length it takes the long hand on your watch to move in a full circle.

If your math class lasts an hour, it might start at 9:30 and end at 10:30, one hour later. Hour also means "time of day." If your phone rings at two a.m., you could ask, "Why are you calling at such a late hour, Mom?" The word stems from the Old French hore, "one-twelfth of a day," with its roots in the Latin hora, "hour" or "season," and Greek hora, "the season."

Definitions of hour
  1. noun
    a period of time equal to 1/24th of a day
    “the job will take more than an hour
    synonyms: 60 minutes, hr
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    sidereal hour
    1/24 of a sidereal day
    man hour, person hour
    a time unit used in industry for measuring work
    type of:
    time unit, unit of time
    a unit for measuring time periods
  2. noun
    distance measured by the time taken to cover it
    “we live an hour from the airport”
    synonyms: minute
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    type of:
    the property created by the space between two objects or points
  3. noun
    clock time
    “the hour is getting late”
    synonyms: time of day
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    high noon, midday, noon, noonday, noontide, twelve noon
    the middle of the day
    the hour at which a meal is habitually or customarily eaten
    late-night hour
    the latter part of night
    12 o'clock at night; the middle of the night
    small hours
    the hours just after midnight
    the time you go to bed
    closing time
    the regular time of day when an establishment closes to the public
    aurora, break of day, break of the day, cockcrow, dawn, dawning, daybreak, dayspring, first light, morning, sunrise, sunup
    the first light of day
    early-morning hour
    an hour early in the morning
    sundown, sunset
    the time in the evening at which the sun begins to fall below the horizon
    crepuscle, crepuscule, dusk, evenfall, fall, gloam, gloaming, nightfall, twilight
    the time of day immediately following sunset
    a canonical hour that is the ninth hour of the day counting from sunrise
    happy hour
    the time of day when a bar sells alcoholic drinks at a reduced price
    rush hour
    the times at the beginning and end of the working day when many people are traveling to or from work
    zero hour
    the time set for the start of an action or operation
    canonical hour
    (Roman Catholic Church) one of seven specified times for prayer
    breakfast time
    the customary or habitual hour for eating breakfast
    lunch period, lunchtime
    the customary or habitual hour for eating lunch
    dinnertime, suppertime
    the customary or habitual hour for the evening meal
    a prescribed bedtime
    a shortening of nightfall
    matins, morning prayer
    the first canonical hour; at daybreak
    the second canonical hour; about 6 a.m.
    terce, tierce
    the third canonical hour; about 9 a.m.
    the fourth of the seven canonical hours; about noon
    the fifth of the seven canonical hours; about 3 p.m.
    evensong, vespers
    the sixth of the seven canonical hours of the divine office; early evening; now often made a public service on Sundays
    complin, compline
    last of the seven canonical hours just before retiring
    type of:
    clock time, time
    a reading of a point in time as given by a clock
  4. noun
    a special and memorable period
    “it was their finest hour
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    type of:
    period, period of time, time period
    an amount of time
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