The short answer

A "second" in time is called a "second" because it is the second division of an hour. The first division of an hour is the minute, which divides an hour into 60 parts. Seconds are the next division, breaking each minute down into 60 smaller units.

The long answer

The etymology of "second" as a unit of time goes back to when the Romans adopted the Babylonian base-60 time system, where each hour is divided into 60 minutes, and each minute is further divided into 60 seconds. The word "second" itself comes from the Latin term "secundus," which means "following" or "second in order." This makes sense when considering that a second follows a minute in the order of time divisions.

Minutes got their name from the Latin "pars minuta prima" (small first part), referring to the first division of an hour. Seconds are called “seconds” because they are the second division of an hour, or "pars minuta secundus".

Therefore, seconds are called "seconds" because they represent the second division of an hour.

🧠 Bonus brain points

Did we ever measure time in "thirds" (1/60 of a second)?

If seconds are called "seconds" because they are the second division of an hour, it raises an interesting question: did we ever use "thirds" (1/60 of a second) as a measurement of time?

The answer is yes, but "thirds" were never commonly used in everyday language. Instead, they were employed in mathematical and scientific contexts as units smaller than a second. Today, we measure time smaller than a second using decimals rather than fractional terms like "thirds."

Why do we have 60 seconds and 60 minutes but only 24 hours?

The root of having 60 seconds and 60 minutes in an hour comes from ancient Babylonian mathematics, where the base-60 system was commonly used. However, the reason we have only 24 hours in a day is due to Egyptian sundials, which were designed to divide daytime into 12 units. It's believed that 12 was chosen either because that's how many lunar cycles are in a year or because 12 is the number of finger joints on each hand (excluding the thumb), making it easy to count.

It's unknown exactly why we landed on 60 minutes and seconds. But one possibility is because 60 is the smallest number divisible by the first six counting numbers (1, 2, 3, 4, 5, 6) as well as by 10, 12, 15, 20, and 30, making it highly practical for division and calculation.

Sources

Harper, D. (2019, January 27). Minute (n.). Etymonline.com. Retrieved April 21, 2023, from  https://www.etymonline.com/word/minute

Harper, D. (2022, March 26). Second (n.). Etymonline.com. Retrieved April 21, 2023, from https://www.etymonline.com/word/second

Lombardi, M. A. (2007, March 5). Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day? Scientific American. Retrieved April 21, 2023, from https://www.scientificamerican.com/article/experts-time-division-days-hours-minutes/

Moxon, J. (1698). A tutor to astronomy and geography. Or, An easie and speedy way to know the use of both the globes ... The fifth edition corrected and enlarged, etc (5th ed.).