What does sennight mean?

Sennight means a week, literally seven nights, from the Old English seofon nihta. It was ordinary English for centuries and appears in Shakespeare and Jane Austen, but it fell out of everyday use during the nineteenth century and is now considered archaic.

Why did sennight disappear but fortnight did not?

English already had week, a shorter and older word for seven days, so the longer synonym was redundant. Nothing comparable existed for fourteen days, and rents, wages and market cycles kept using that unit, which held the word in circulation.

Why do fortnight and sennight count nights instead of days?

Early Germanic peoples reckoned time from nightfall rather than sunrise, and English inherited the habit. The same convention survives in tonight, overnight and Twelfth Night, and in the way the eve of a feast comes before the feast itself.

Sennight: The Lost Word for a Week

Q: What were the English quarter days?

They were the four dates on which rents fell due and servants were hired: Lady Day on 25 March, Midsummer on 24 June, Michaelmas on 29 September and Christmas on 25 December. Scotland used a separate set called term days.

English kept one half of a matched pair and threw the other away. A fortnight is fourteen nights, and for most of the language's history it had a smaller companion: a sennight, seven nights, meaning a week. The word was ordinary, unremarkable and in constant use for a thousand years, and then within a couple of generations it was gone, leaving the longer unit standing alone with nothing to explain its shape.

This article covers what the word meant, why it died while its sibling survived, and the other units of time English has quietly discarded along the way. If you want the surviving unit rather than the lost one, the current fortnight tracker shows which fortnight of the year is running and how much of it is left.

What Was a Sennight?

A sennight was seven nights, that is to say a week. It came from the Old English seofon nihta and was written variously as sennight, se'nnight and sev'night, the apostrophe marking the swallowed syllable in the middle.

It was in no sense a poetic or specialist term. People arranged to meet in a sennight the way they might now say next week. The word appears throughout Middle English, sits comfortably in Shakespeare, and was still natural in the letters and novels of the early nineteenth century. Jane Austen used it without a flicker of self-consciousness. By the end of that century it had all but vanished from ordinary speech, and it survives now only as an antiquarian curiosity.

Why Sennight Died and Fortnight Survived

Because English already had a perfectly good short word for seven days and none at all for fourteen. Week, from the Old English wice, was shorter, older and unambiguous, so the longer synonym had no work left to do; the fourteen-day unit faced no such competitor.

Institutions helped. Rents, hiring, wages and market cycles were routinely reckoned in fourteen-day blocks, so the word stayed in ledgers and contracts long after it might otherwise have drifted out of speech. Redundancy kills a word faster than anything else, and a sennight was redundant from the moment week became standard. It is the same pressure that keeps fortnight healthy in Britain, Ireland, Australia, New Zealand and India while American English, which found the alternatives two weeks and biweekly good enough, let it lapse; that divergence is traced in fortnight in British and Australian English.

Counting Time in Nights

Both words are built on nights rather than days, which is not an accident of style. Early Germanic peoples reckoned spans of time from nightfall, a habit Roman writers recorded with some surprise, and English inherited the convention before gradually abandoning it.

Traces are everywhere once you look. Tonight, overnight, yesternight and Twelfth Night all count in the older manner, and the eve of a feast still precedes rather than follows it. Other languages made different choices from the same raw material. French counts a week as huit jours, eight days, and a fortnight as quinze jours, fifteen, because the count includes both the starting day and the finishing one. The units are identical; only the counting convention differs, which is exactly the trap that catches people calculating notice periods today.

Other Lost Units of Time

English has shed a good deal more than one word for a week. These are the discarded units most worth knowing:

Twelvemonth: a year, once as common as fortnight and now surviving mainly in the legal phrase a year and a day.
Hebdomad: a period of seven days, borrowed from Greek and used in learned and ecclesiastical writing where week would have done.
Octave: the eighth day after a church feast, counted inclusively, which in practice means a week later. Still used in liturgical calendars.
Nundinum: the Roman market cycle of eight days, called the ninth day because the Romans counted both ends. Rome ran on this rhythm before the seven-day week arrived.
Kalends, Nones and Ides: the three anchor points of the Roman month, with dates reckoned backwards towards the next anchor rather than forwards from the first.
Lustrum: five years, the interval between Roman censuses.
Indiction: a fifteen-year tax cycle used for dating documents across the late Roman and Byzantine world for centuries.
Watch: a four-hour period at sea, and before that a division of the night; a ship's bell still marks the half-hours within one.

The Quarter Days and Term Days

Before the modern calendar of monthly billing, the year in England, Wales and Ireland turned on four quarter days: Lady Day on 25 March, Midsummer on 24 June, Michaelmas on 29 September and Christmas on 25 December. Rents fell due, servants were hired and accounts were settled on those dates.

Scotland used a different set of four term days, Candlemas, Whitsunday, Lammas and Martinmas, spaced through the year on the same principle. These were units of time in the practical sense that a fortnight is one: they defined the intervals people actually planned around. Their disappearance from everyday speech, much like the loss of the seven-night word, reflects the shift to a calendar governed by monthly salaries and monthly bills rather than by feast days and harvests.

Where the Old Words Still Survive

Several of them are hiding in plain sight. Michaelmas still names the autumn term at Oxford and Cambridge and the first term of the English legal year. Lady Day sits behind the odd start date of the British tax year, which begins on 6 April rather than 25 March because of the eleven days dropped in the calendar reform of 1752 and a further adjustment in 1800.

The fourteen-day unit is the healthiest survivor of the group, and it survives because it is still doing a job: pay runs, rent, refuse collections, sprints and rotas all run on it. Words persist when they are useful and fade when they are ornamental. For the surviving unit's definition and arithmetic, see what is a fortnight, or work out how many of them fit in a year in how many fortnights in a year. To add or subtract intervals from a date directly, use the fortnight calculator.

Conclusion

A sennight was seven nights, an everyday word for a week that lasted from Old English to the nineteenth century and then dropped out because week said the same thing in one syllable. Its longer sibling survived because nothing else covered fourteen days and because ledgers and leases kept using it. The twelvemonth, the hebdomad, the octave, the lustrum and the quarter days went the same way as the sennight, useful once and ornamental afterwards. To see the one unit that made it through still in use, open the current fortnight tracker or explore fortnight.now.

Sennight and Other Lost Time Words of English