From Sabbath to sábado
Moving on to the weekend now, the Spanish word for Saturday, namely sábado, does not come from the name for this day in Classical Latin. Despite the coincidence of the two initial letters, the words Saturday and sábado are not in any way related either. The English word Saturday, on the other hand, is related in an interesting way to the Classical Latin name for this day of the week.
The original name for this day in Classical Latin was diēs Saturnī ‘day of Saturn’ (Lat. Saturnī is the genitive case wordform of nominiative Saturnus ‘Saturn’). The English name, Saturday, is a calque of the Latin name, as we shall see (cf. §20.9 below). However, the name for the last day of the week in Spanish comes ultimately from Hebrew. The change happened first in Ecclesiastical Latin, where this day came to be called sabbatum, which is a loanword from Biblical Greek σάββατον (sábbaton), which is an loan from Biblical Hebrew שַׁבָּת (shabát). This Hebrew word meant ‘weekly day of rest’ and it is derived from the Hebrew verb shâbath ‘to stop [working], to rest’, which may itself come from Acadian, an East Semitic language spoken in ancient Mesopotamia. From the same Hebrew root comes the verb שָׁבַת (shavát), meaning ‘to cease, to stop (working), to rest’ (as well as ‘to go on strike’ in modern times).
In the Jewish religious tradition, from which the Christian and Muslim religious traditions stem, the šabbāt was the last day of the week and the day of rest. The word has been borrowed into English as Sabbath, which can mean ‘the seventh day of the week, Saturday, observed as the day of rest and worship by the Jews and some Christian sects’ (AHD). It can also refer to Sunday, however, which is the day of rest and worship for most Christians.
Nowadays, even in the Christian world there is variation as to whether Saturday is considered the last day of the week, as it was traditionally conceived. That is the way it is in some ways conceived in the United States, for instance, for calendars show Saturday as the last day of the week (and Sunday as the first). This clashes, however, with the modern notion of the weekend (Sp. fin de semana), in which Saturday and Sunday are considered a unit that follows the work week and thus end it. In most parts of the world, including most of the Spanish speaking world, calendars show Sunday, not Saturday, as the last day of the week, grouping the two weekend days together.
Eng. sabbatical ~ Sp. sabático
The word sábado is related to a word that refers to a pair of cognate words: Eng. sabbatical and Sp. sabático. These words refer to ‘a period when someone, especially someone in a university job, stops doing their usual work in order to study or travel’ (DOCE). It is a period of rest from teaching that (mostly) academics enjoy. These words come from Late Latin adjective sabbaticus ‘of the Sabbath’, formed with the adjectival suffix ‑ic‑ (sabbat‑ic‑us) )‑ added to the Latin root sabbat‑. English even added a second adjectival suffix, the Latinate ‑al‑, to the word when it borrowed it in the 17th century. These words can still be used as adjectives, but nowadays they can be used also as nouns. Thus you can speak of a sabbatical year or just of a sabbatical, cf. Sp. (año) sabático.
Saturday in other Romance languages
There was another way to render the new day of the week in Latin besides sabbatum, namely as sabbatī diēs or diēs sabbatī ‘day of the Sabbath’ (sabbatī was the genitive case wordform of the word sabbatum). Romance languages that did not drop the diēs part of the Latin name of the day of the week like Spanish did, also retain it here.
Thus, in Catalan, Saturday is dissabte [di.ˈsap.tə], a contraction of Latin diēs sabbatī. In French, Saturday is Samedi [sam.ˈdi], from an earlier sambedi, from Vulgar Latin *sambati dies ‘day of the Sabbath’. (This sambati was a variant of sabbatī). The Standard Italian word for Saturday is sabato /ˈsa.ba.to/, from the same source as Spanish sábado, namely Church Latin nominative (and accusative) sabbatum.
The name that sabbatum replaced was diēs Saturnī ‘day of Saturn’. Saturn was a very important and complex god in the Roman pantheon. It was originally the god of agriculture. However, in classical times the Romans equated this god with the Greek’s god Κρόνος (krónos), the Titan of the Harvest, a name Latinized as Cronus, and by this association, it acquired additional chracteristics, which show up in Roman literature and art. For instance, Cronus was sometimes associated with the word Xρόνος (chronos) ‘time’, though the words are not related, and so is Saturn.
Not surprisingly, the name of the equivalent day of the week in Greek was ἡμέρᾱ Κρόνου (hēmérā Krónou) ‘day of Chronos’. The Romans named the last day of the week and the sixth planet from the sun (the outermost of the planets that are visible with the naked eye) after this god. A week-long festival in the honor of the god was held in the middle of December known as Saturnalia. It was ‘a time of general unrestrained merrymaking, extending even to the slaves’ (OED).
 in Greek mythology, Cronos was the father of Zeus (the Roman Jupiter) and was deposed by him. Cronus had himself usurped his father Uranus’s position as ruler of the universe by cutting off his testicles. During the Renaissance, ancient Greek myths were back in vogue and the association came back between Cronos and Chronos, resulting in the figure of Father Time , a personification of time ‘as a very old man carrying a scythe and an hourglass’ (RHWC).
 The Saturnalia was ‘a time of feasting, role reversals, free speech, gift-giving and revelry’ (WP). The noun Sātŭrnālĭa is derived from an identical plural adjective wordform (sing. Saturn-āl-is) that meant ‘of Saturn’. It was derived from the noun saturnus (saturn-us) and the adjectival suffix ‑āl‑, which created third declension adjectives, whose nominative and genitive singular masculine and feminine inflectional ending is ‑is. The etymology of the word Saturn is not known, but it does not seem to be an Indo-European word. More likely it is Etruscan, cf. the Etruscan god Satre.