The names of the days of the week in Spanish and English do not seem very much alike — so you may be surprised to find out they have similar origins. Most of the words for the days are tied to planetary bodies and ancient mythology.

Key Takeaways Days of the week in Spanish are masculine and not capitalized.

The names of the five weekdays in English and Spanish are connected to each other, coming from astronomy and mythology.

The names of the weekend days in English and Spanish have different origins in the two languages.

Also, the English and Spanish names for the name of the seventh day of the week, "Saturday" and sábado, aren't related at all even though they look vaguely similar.

The names in the two languages are:

Sunday: domingo

Monday: lunes

Tuesday: martes

Wednesday: miércoles

Thursday: jueves

Friday: viernes

Saturday: sábado

History of the Days of the Week in Spanish

The historical origin or etymology of the days of the week can be linked to Roman mythology. The Romans saw a connection between their gods and the changing face of the nighttime sky, so it became natural to use their gods' names for the planets. The planets the ancient people were able to track in the sky were Mercury, Venus, Mars, Jupiter, and Saturn. Those five planets plus the moon and sun made up the seven major astronomical bodies. When the concept of the seven-day week was imported from Mesopotamian culture early in the fourth century, the Romans used those astronomical names for the days of the week.

The first day of the week was named after the sun, followed by the moon, Mars, Mercury, Jupiter, Venus, and Saturn. The names of the week were adopted with little change throughout most of the Roman Empire and beyond. In only a few cases were changes made.

In Spanish, the five weekdays all retained their planetary names. Those are the five days whose names end in -es, a shortening of the Latin word for "day," dies. Lunes comes from the word for "moon," luna in Spanish, and the planetary connection with Mars is also apparent with martes. The same is true with Mercury/miércoles, and Venus is viernes, meaning "Friday."

The connection with Jupiter is not quite so apparent with jueves unless you know Roman mythology and recall that "Jove" is another name for Jupiter in Latin.

The days for the weekend, Saturday and Sunday, were not adopted using the Roman naming pattern. Domingo comes from a Latin word meaning "Lord's day." And sábado comes from the Hebrew word "sabbath," meaning a day of rest. In Jewish and Christian tradition, God rested on the seventh day of creation.

Stories Behind the English Names

In English, the naming pattern is similar, but with a key difference. The relation between Sunday and the sun, Monday and the moon and Saturn and Saturday are obvious. The celestial body is the root of the words.

The difference with the other days is that English is a Germanic language, unlike Spanish which is a Latin or Romance language. The names of equivalent Germanic and Norse gods were substituted for the names of the Roman gods.

Mars, for example, was the god of war in Roman mythology, while the Germanic god of war was Tiw, whose name became part of Tuesday. "Wednesday" is a modification of "Woden's Day." Woden, also called Odin, was a god who was swift like Mercury. The Norse god Thor was the basis for naming Thursday. Thor was considered an equivalent god to Jupiter in Roman mythology. Norse goddess Frigga, after whom Friday was named, was, like Venus, the goddess of love.

Using the Days of the Week in Spanish

In Spanish, the names of the week are all masculine nouns, and they are not capitalized except at the beginning of a sentence. Thus it is common to refer to the days as el domingo, el lunes, and so on.

For the five weekdays, the names are the same in singular and plural. Thus we have los lunes, for "Mondays," los martes for (Tuesdays), and so on. The weekend days are made plural just by adding -s: los domingos and los sábados.

It is very common to use the definite articles el or los with the days of the week. Also, when talking about activities taking place on a certain day of the week, the "on" of English is not translated. So "Los domingos hago huevos con tocino" would be a common way of saying "On Sundays I make eggs with bacon."