1. One of the 24 equal parts of a day.
a. One of the points on a timepiece marking off 12 or 24 successive intervals of 60 minutes, from midnight to noon and noon to midnight or from midnight to midnight.
b. The time of day indicated by a 12-hour clock.
c. hours The time of day determined on a 24-hour basis: 1730 hours is 5:30 PM.
3. A unit of measure of longitude or right ascension, equal to 15° or 1/24 of a great circle.
a. A customary or fixed time: the dinner hour.
b. hours A set or customary period of time for a specified activity: banking hours.
a. A particular time: their hour of need.
b. A significant time: Her hour had come.
c. The present time: the man of the hour.
a. The work that can be accomplished in an hour.
b. The distance that can be traveled in an hour.
a. A single session of a school day or class.
b. A credit hour.
8. hours Ecclesiastical The canonical hours.
A longer than usual or customary period of time for a given activity: worked long hours to finish the project on time.
[Middle English, from Old French houre, from Latin hōra, from Greek hōrā, season, time; see yēr- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.