Why Menstruation Means Moon

Say the word slowly: menstruation. It sounds clinical, like something printed on a box in the pharmacy aisle. But hidden inside it is the word month, and hidden inside month is the moon. Every time a doctor’s form asks for the date of your last menstrual period, it is asking, without knowing it, about the moon.

That is the short answer to the question. Menstruation “means moon” because the word descends from the Latin for month, and the English words month and moon share an ancient root. The longer answer is a story about how people told time, what they saw in the sky, and why the body and the moon ended up in the same sentence in so many languages.

The word hiding in the word

English “menstruation” comes from the Latin menstruus, monthly, which comes from mensis, month. The Romans were not being poetic. They were being accurate: this is the thing that happens monthly. The same Latin root sits in quieter corners of English too, anywhere something is counted by the month.

So the first layer is simple. Your period was named for its rhythm. Long before anyone understood hormones, people understood that this came around again, and that it came around on roughly the same schedule as something else they could see every night.

Month and moon, one root

Go back further and the two words meet. “Month” and “moon” share an ancient root, which is why they still look like siblings on the page. The Greeks called the moon mēnē, and Mene was also the name of a Greek moon goddess. A month, in the oldest sense, was a moon: the stretch of time from one new moon to the next.

That stretch is about 29.5 days, the Moon’s synodic cycle. When you live without printed calendars, it is the most obvious clock there is. You can watch it fatten and thin. You can count on it. It is no surprise that the word for the month grew out of the word for the moon, or that the word for monthly bleeding grew out of the word for the month.

月经: the moon in another language

The link is not only European. In Chinese, a period is 月经, yuèjīng. The first character, 月, means moon, and it also means month. The second, 经, carries the sense of a regular course or passage. Read literally, a period is the moon’s regular passage.

There is something quietly lovely about that. It doesn’t say the moon causes the bleeding. It says the bleeding keeps a course, the way the moon does. Two languages with no shared ancestry arrived at the same picture: a body keeping time alongside the sky.

When the moon was the calendar

Many cultures linked the moon and the month, and it is easy to see why. Before clocks and apps, you kept track of time by watching things that repeat: seasons, tides, the moon. A cycle of around a month was one of the few long rhythms a person could feel in their own body, and the moon was the one long rhythm anyone could see.

It is worth being careful here. The internet is full of confident claims about what “ancient women” did with the moon, and most of them are invented or flattened. What we can say honestly is general: across many places and centuries, people noticed that the moon and the body both kept a roughly monthly count, and their words remember that noticing.

The goddesses who kept the link

Myth gave the link a face. Selene, in Greek myth, was the Moon itself, crossing the night sky. Artemis, who came to be linked with the Moon, was a protector of women and of childbirth, a fierce figure who belonged to the wild places and to the thresholds of women’s lives.

Among the Maya, Ix Chel was a goddess associated with the Moon, childbirth, fertility and weaving. That last one is worth sitting with. Weaving is patient, repeated, rhythmic work, thread over thread, and a cycle is a kind of weaving too: the same pattern, never exactly the same. We tell more of these stories in the moon goddesses of the cycle.

What astrology inherited

Traditional astrology carried the old link forward and gave it a structure. In astrology the Moon rules the body’s fluids and tides, fertility, nourishment, mothering and the rhythms of the month. It governs the emotional body. It rules Cancer, the crab who carries home on its back, and it is associated with the 4th house, the part of the chart that describes roots and private life.

So when an astrologer talks about your Moon, they are drawing on the same instinct that built the word menstruation: that there is a monthly, tidal, bodily layer of a person, and that the moon is its emblem. Your own natal Moon sign is one way to describe how you meet that layer, which we explore in your moon sign and your period.

Is the link literal?

Here is where Feya stays honest. The words record a real observation: the moon’s cycle is about 29.5 days, and many menstrual cycles are close to that. But cycles on average run from about 21 to 35 days, and they vary. When the period app Clue looked at 7.5 million cycles, period start dates fell randomly across moon phases.

A few small studies have found that some people’s cycles line up with the moon for stretches of time, especially with less artificial light at night. It is a fascinating question, and we give it a careful look in does the moon affect your period. But the language did not come from a lab. It came from people paying attention, and paying attention is still the best thing it can teach you.

A small practice with old words

You don’t need to believe the moon runs your body to enjoy knowing that your body’s oldest name is a moon word. Let the etymology be a reminder that you belong to a very long line of people who looked up and counted.

Try this at the start of your next period. Before you open an app, find the moon, through a window or on a walk to the car. Say its phase out loud, even under your breath: waxing, full, waning, new. Then write the date and the phase at the top of a page, and let yourself write for five minutes under it. You are doing what the word menstruation remembers: keeping count by the sky.

What did I learn about my period growing up, and what words did the people around me use for it?

If I named my cycle after something I can see, what would I name it?

What would change if I thought of this week as a passage rather than an interruption?

Feya is for reflection, not medical advice. Cycle tracking is not birth control, and changes in your period are worth raising with a doctor.

Related

• The Moon and Your Cycle
• The Goddesses Who Kept the Month
• Does the Moon Affect Your Period? The Honest Answer
• What Your Moon Sign Needs When You Bleed