Every week, without realizing it, you summon a pantheon of ancient gods. Tuesday belongs to a one-handed war god, Wednesday to the wandering Odin, Thursday to thunder-wielding Thor. And every year you march through a calendar built by Roman emperors and deities. The names of our days and months are the oldest religion still spoken aloud. This is their etymology.
The Seven Days: Gods of Two Pantheons
The seven-day week came to northern Europe from Rome, where the days were named after the sun, the moon, and the five visible planets — themselves named for gods. When the names reached the Germanic-speaking world, four of the Roman gods were swapped for their nearest Norse and Germanic equivalents. The result is a fascinating hybrid: a Roman framework wearing Viking clothing.
| Day | Named after | Roman equivalent |
|---|---|---|
| Sunday | the Sun | dies Solis |
| Monday | the Moon | dies Lunae |
| Tuesday | Tiw / Tyr (war god) | Mars (dies Martis) |
| Wednesday | Woden / Odin | Mercury (dies Mercurii) |
| Thursday | Thor (thunder) | Jupiter (dies Jovis) |
| Friday | Frigg / Freya | Venus (dies Veneris) |
| Saturday | Saturn | dies Saturni |
The Romance languages kept the Roman gods intact, which is why the kinship is clear when you compare them: French mardi (Mars), mercredi (Mercury), jeudi (Jupiter), and vendredi (Venus) match the English Tuesday, Wednesday, Thursday, and Friday god-for-god — only the gods’ names differ. Saturday alone kept its Roman name in English (Saturn), while the Romance languages renamed it for the Sabbath (French samedi).
The Months: An Emperor’s Calendar
The months are pure Rome, a mixture of gods, festivals, emperors, and plain numbers. The Roman year originally began in March, a fact that explains one of the calendar’s great oddities — the “wrong” numbers at the end.
| Month | Named after |
|---|---|
| January | Janus, two-faced god of doorways and beginnings |
| February | Februa, a Roman purification festival |
| March | Mars, god of war (the old start of the year) |
| April | perhaps Aphrodite, or Latin aperire, “to open” (buds) |
| May | Maia, goddess of growth |
| June | Juno, queen of the gods |
| July | Julius Caesar |
| August | Augustus, the first emperor |
| September–December | the numbers 7, 8, 9, 10 (septem, octo, novem, decem) |
The Mystery of the Misnumbered Months
Why is September — from the Latin for “seven” — the ninth month? Why is December (“ten”) the twelfth? Because the original Roman calendar began in March. Count from there and the numbers line up perfectly: September was the seventh month, October (“eight,” like octopus) the eighth, November (“nine”) the ninth, and December the tenth. When January and February were later added to the start of the year, the numbered months were shoved two places down — and never renamed. Two thousand years later, we still live with the bookkeeping error of the ancient Roman state.
Hidden Time Words
The vocabulary of time is full of buried images. Calendar comes from the Latin kalendae, the first day of the month, when debts were called in and accounts (“calends”) were settled. A month is literally a “moon,” the period of one lunar cycle. Noon originally meant the “ninth hour” (Latin nona) of the Roman day — about 3 p.m. — but the meal associated with it drifted earlier over the centuries until noon settled at midday. And the word day itself, like dawn, traces back to an ancient root meaning “to burn” — the daily kindling of the sun.
Why Seven Days, and Other Time Puzzles
The seven-day week is not astronomical — nothing in the sky repeats every seven days. It comes instead from Babylonian astronomy, which counted seven “wandering stars” (the sun, moon, and five visible planets), reinforced by the seven-day creation account of the Hebrew Bible. Rome spread the system across Europe, and it has ticked on unbroken ever since — one of the oldest continuously used human inventions.
Other corners of the calendar hide their own etymologies. A.M. and P.M. are Latin — ante meridiem and post meridiem, “before” and “after midday.” The Julian calendar is named for Julius Caesar, who reformed it in 46 BC; the Gregorian calendar we use today is named for Pope Gregory XIII, who corrected its drift in 1582. A leap year “leaps” because adding a day in late February makes each fixed date jump forward two weekdays instead of one. And the very word season comes from the Latin satio, “a sowing” — the farmer’s year hiding inside the calendar.
| Time word | Origin | Literally |
|---|---|---|
| calendar | Latin kalendae | the day debts were “called” due |
| month | Old English monath | a “moon” cycle |
| noon | Latin nona (hora) | the “ninth hour” — once about 3 p.m. |
| season | Latin satio | “a sowing” |
| week | Old English wicu | linked to “turning, succession” |
Frequently Asked Questions
Why are the English and French weekday names so different yet parallel?
Both descend from the Roman planetary week. The Romance languages kept the Roman gods (Mars, Mercury, Jupiter, Venus), while English substituted the equivalent Germanic and Norse gods (Tiw, Woden, Thor, Frigg). The framework is identical; only the names of the gods were translated.
Why does September mean “seven” but fall ninth?
The early Roman calendar started in March, making September the seventh month. The later insertion of January and February at the start pushed the numbered months out of place, and they were never renamed.
Keep Exploring
- The Norse gods in the week → Old Norse in English
- The Roman roots of the months → Latin Root Words
- Browse every theme → Etymology by Domain
- More astonishing word histories → Word Origin Stories