My son asked me the other day what a.m. and p.m. mean. Of course I could tell him what they mean, but what do those letters stand for. Turn’s out they’re Latin of course! My first guess for p.m. was close, “post meridian” but couldn’t come up with the a.m. A.M. is ante meridiem (a.m., from Latin, literally “before midday”) and post meridiem (p.m., “after midday”).
Other great time related info courtesy of the US government