Here's how it evolved:
* "Sexta" in Latin meant "sixth".
* During the medieval period, "sexta" came to refer to the sixth hour after midday, which was around 1 pm. This was a common time for a break during the hot afternoon sun.
* Over time, the term "sexta" evolved into the Spanish "siesta" to specifically denote the midday nap.
Therefore, the word "siesta" originated from the Latin word for "sixth" and its association with the sixth hour after midday, a traditional time for a midday nap in many cultures.