The hour clock is a time convention in which the 24 hours of the day are divided into two periods: a. The hour clock was developed from the middle of the second millennium BC to the 16th century AD. The hour time convention is common in several English-speaking nations and former British colonies, as well as a few other countries.

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What does “a.m.” mean?
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Midnight and Noon: AM or PM?
Some countries, including the US, Canada, and Australia, use the hour clock format including am and pm. What do these abbreviations mean? Is midnight am or pm?
Entry 1 of 5 present tense first-person singular of be Am. Accessed 13 Nov. Keep scrolling for more More Definitions for am AM. Entry 1 of 2 americium AM.