- Of or according to the clock: three o'clock. (adverb)
- According to an imaginary clock dial with the observer at the center and 12 o'clock considered as straight ahead in horizontal position or straight up in vertical position. Used to indicate relative position: enemy planes at 10 o'clock. (adverb)
- Used after a number from one to twelve to indicate the hour of the day or night (adverb)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
- Used after a number to indicate direction or position relative to the observer, twelve o'clock being directly ahead or overhead and other positions being obtained by comparisons with a clock face (adverb)
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