1. before noon.2. the period from midnight to noon, esp. the period of daylight prior to noon: Shall we meet Saturday a.m.?3. a morning newspaper, sometimes issued shortly before midnight. Cf. p.m.[L ante meridiem]Usage. The abbreviation A.M. for Latin ante meridiem, meaning "before noon," refers to the period from midnight until noon. One minute before noon is 11:59 a.m. One minute after noon is 12:01 p.m. Many people distinguish between noon and midnight by saying 12 noon and 12 midnight. Expressions combining A.M. with morning (6 a.m. in the morning) and P.M. with afternoon, evening, or night (9 p.m. at night) are redundant and occur most often in casual speech and writing. Both a.m. and p.m. sometimes appear in capital letters, especially in printed matter.
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