Why is a second called a second?
The short answer
A second in time is called a “second” because seconds are the second division of an hour. The first division of an hour is, of course, minutes.
The long answer
The origin of the word “second” traces back to when Romans adopted the Babylonian invention of a base-60 time system, in which each hour is divided into 60 minutes and each minute is divided into 60 seconds. The term "second" as a unit of time is derived from the Latin word "secundus," which means "following" or "second in order."
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".
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Did we ever measure time in "thirds" (1/60 of a second)?
If we call seconds because they're the second division of an hour, it follows that we may have referred to the third division of an hour (1/60 of a second) as thirds.
In fact, this is true, however "thirds" was not used colloquially, only in mathematic and scientific circles as units of measurements. Now we measure time smaller than a second in decimals, rather than fractions.
Why do we have 60 seconds and 60 minutes but only 24 hours?
The root of 24 hours comes from Egyptian sundials, which were designed to divide the hours of sunlight into 12 units. It's thought 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.
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.
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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.).
