The word siesta was first used in 1655 with the same meaning and spelling as today. It was borrowed from Spanish, and the Spanish word developed from the Latin phrase sexta hora, which literally translates to "sixth hour" but was practically used to refer to noon time, the sixth hour after sunrise according to the Roman timekeeping system, when people would take their naps. The sexta part, which we are concerned with here, is the female version of sextus, meant "six" and is also the etymon of the words sextuple, sextile, sestina, and sextet, and the name Sistine Chapel (which was named after Pope Sixtus IV). Going back even further, sextus is reconstructed to Proto-Indo-European sweks, which also meant "six". According to Google NGram Viewer, usage of siesta has had its ups and downs and has recently been on the rise again.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.