Why is there a circumflex accent on "dîner"?

Why is there a circumflex accent on dîner? I know that in most cases it replaces a missing “s” but what’s the story with this word?

I know I said that I usually don’t respond to language questions, but I just love talking about circumflex accents (and I’ll use this as an excuse to teach you a thing or two about the history of the French language).

First of all, Shea, you are right, the circumflex accent replaces a missing “s” that used to be there in old French and that is still there in English. Think forêt and forest, hôpital and hospital, etc.
So, what’s the deal with dîner, one does not say to disne, neither disnner in English?
Thing is that the circumflex accent still replaces a missing “s” but from a very long time ago.

See, all of these words that have lost their “s” in French but not in English have lost them quite recently, most of the time in the late Middle Ages, after William the Conqueror imported French to England (and the “s” in those words with it) in 1066.

And dîner comes from disjejunare in Latin which means “to stop fasting.” The prefix “dis” with this meaning of stop is not uncommon in English, we find it in many words (most of the words starting with “dis” actually).
You’ll also notice that the verb déjeuner (to have lunch) comes from the same Latin verb and is almost a literal translation of “to stop fasting”

So in the case of this word, the “s” disappeared quite early in the language (most certainly before the Norman Invasion) but the circumflex accent is there.
I actually assume that it appeared on the word much later than the disappearance of the “s”, but it’s just an assumption.

And this is my excuse to tell you about the history of the circumflex accent, because, you see, accents in French are not there for cosmetic reasons only, they have a use other than just putting it on a random letter to look French in English marketing.

For that, we need to go back in time during the Middle Ages. I know it’s a time period that’s blurry at best for most Americans, but just do some research if it’s too blurry, I can’t tell you all about medieval times right now (no, there were no dragons back then despite what Mickey Mouse wants you to believe).
So, during the Middle Ages, Guttenberg hadn’t been born yet and China was more or less unknown, so to reproduce written documents people used monks.
Yep, there were monks everywhere at the time and as they just can’t spent 24 hours a day praying there was a need to find them something to do with their times. So they used to copy books by hand, which was kinda handy as they usually were the only ones that could write in the population and so the copying monks (which were not all monks, some were brewing beer too, and then we have people saying that monks are useless when they brought us the best things in life: books and booze) copied books…

And one can say that there were two types of copying monks.
The docile ones and the rebellious ones.
The docile ones were the ones that just were going on about their business, copying books without bothering anybody. And as a consequence none of them left their name down in history.
The rebellious ones didn’t leave their names down in history either, but they definitely left their marks, especially in the French language (not only the French language, but this is the one that has our interest right now). Why is that?

Let me give you an example.
Let’s take the word hospital. Back in the days, as previously mentioned it was spelled and pronounced the same way in French and English. But little by little things changed in France and little by little the “s” disappeared in the pronunciation.
But the docile monks, doing their job the way they were taught kept on writing hospital fully knowing that it was not pronounced this way.
Also remember that we’re Centuries before Du Bellay and his friends went on their ego trip that totally messed up French spelling as well as Centuries before Richelieu invented the French Academy that froze French spelling in time regardless of the way words actually sound.
Nope, at that time, things tended to be written the way there were pronounced without much ado about it.
Still, shy monks, certainly afraid to be yelled at didn’t dare to drop that “s” from hospital.
But one day, one who was more courageous and/or rebellious decided “to hell with it, it’s been a long time that this “s” is not being pronounced anymore, I’m getting rid of it!” And so did he.
From then on, hospital was going to be written hopital.
Except that it didn’t exactly happened like that.
Did he suddenly have remorse? Did his superior caught him in the act, chastised him?
We don’t know, but suddenly he felt like that “s” had to be honored and remembered because that would be unfair to just make it disappear in limbo. So he decided to add the circumflex on the previous letter a bit like a memorial. And then the thing spread, maybe because the superior told everyone to do the same, maybe because the next monk copying from that monk just copied the thing without thinking twice about it. And the new fashion also spread to other words that had vanishing “s”.

And there we had it… The circumflex accent was a part of the French language and was here to stay.