hour
noun
[ ˈaʊə ]
• a period of time equal to a twenty-fourth part of a day and night and divided into 60 minutes.
• "an extra hour of daylight in the winter evenings"
• a time of day specified as an exact number of hours from midnight or midday.
• "the clock in the sitting room struck the hour"
• a fixed period of time for an activity, such as work, use of a building, etc.
• "the dinner hour"
• (in the Western (Latin) Church) a short service of psalms and prayers to be said at a particular time of day, especially in religious communities.
• "an organized life of prayer including the canonical hours"
• 15° of longitude or right ascension (one twenty-fourth part of a circle).
Origin:
Middle English: from Anglo-Norman French ure, via Latin from Greek hōra ‘season, hour’.
on the hour
• at the same time every hour, or at the beginning of each hour.
• "news bulletins all day on the hour"