Latin Terms Still Ticking Through Our Daily Lives

It’s not every day you use Latin, right? Would you believe that Latin, from ancient Rome, is referenced by almost everyone, many times a day? Have you ever heard the term “ante meridiem?” What about “post meridiem?”

We reference these two terms whenever we write or say “a.m.” or “p.m.”

• a.m. (ante meridiem) means ‘before midday’ in Latin. It refers to the time from midnight (12:00 a.m.) up to just before noon (11:59 a.m.).
• p.m. (post meridiem) means “after midday,” covering the time from noon (12:00 p.m.) to just before midnight (11:59 p.m.).

We use these abbreviations daily, yet most of us never stop to consider their meaning.

Ancient Rome relied heavily on sundials, and midday (meridiem) was marked when the sun reached its highest point, causing the shadow cast by the sundial to be at its shortest. This moment occurs when the sun crosses the local meridian, an imaginary line running north-south. This is known as solar noon (which they always referred to as meridian).

Their day was divided into 12 daylight hours and 12 nighttime hours, but the lengths of these hours varied. For example, during winter, when days are shorter, the winter hours are also shorter than the summer hours. Meridiem always referred to the point of solar noon, regardless of the length of the hours or days, and solar noon always determined whether the time was ante meridiem or post meridiem. Unlike our standardized 12:00 noon, solar noon in Rome could shift by up to 15 minutes, depending on the season, due to the sun’s natural rhythm.

The ancient Romans also relied heavily on water clocks, which are fascinating because they measured time by the controlled flow of water. They were also used by the Greeks, Chinese, and the earliest known Egyptian ones, dating back around 1500 BC. Water clocks helped Romans track a.m. and p.m. hours when sundials weren’t practical, like at night or indoors.

A water clock typically consisted of a container with a small hole or spout, and time was measured by the duration it took for water to either drain or fill to a marked level. Roman water clocks were often ornate, featuring decorative elements or automated figures that moved as water flowed, much like early analog clocks with a touch of flair. They focused more on functionality and status than on precision.

By the 13th century, mechanical clocks powered by weights and gears started to replace water clocks, offering more reliable timekeeping for towns and monasteries.

Our modern 12-hour clock has roots in medieval European mechanical clocks, which adopted the 12-hour divisions of day and night from the Roman system. Unlike a sundial, which uses shadow to tell time, the mechanical clock was designed to provide consistent timekeeping, emphasizing symmetry and ease of use. Instead of pointing north at midday like a sundial’s shadow, the clock’s hands point straight up at 12:00 for symmetry, not to imitate the sun. It appears to be more of an extension of tradition, with 12-hour divisions and the use of a.m. and p.m. continuing through the mechanical era.

By the 14th to 15th century, fixed hours and the 12-hour format became standard in Europe. Through all of these major changes, ante and post meridiem remained.

The terms a.m. and p.m. are direct holdovers from Roman sundial-based timekeeping, making them a 2,000-year-old linguistic artifact in our daily lives!