From a reader…
QUAERITUR:
You occasionally discuss what the plural of gin and tonic should be. I have a similar problem with what you have just assembled. In England, we borrow the French term Prie Dieu. That’s fine in the singular, but what on earth would you call several?
Given the present state of things in the Church and the world, I am relieved to have something important to think about.
Yes, I have written and polled about the plural of that wondrous drink, the “Gin & Tonic”. There is a correct answer, by the way. And also, by the way, I have now made my own batch of tonic!
As for prie-dieu… this is tough, because it’s, you know, French. They don’t make it easy.
From the English point of view, I think the plural could be invariable: prie-dieu.
However, we find also prie-dieus and prie-dieux.
Webster and Oxford seem to favor the later, though Dictionary.com shows both.
I say…. and this could be the official ruling after I ponder this… that words ending with an “x” for plural are cooler than those that don’t.
THAT SAID… we want to avoid even the suggestion of polytheism.
Let’s have a poll. Anyone can vote, but you have to be registered and approved to comment.

I voted for prie-dieux because it seems to me to be the most common in English writers.
But the French plural is prie-Dieu (invariable; note the capital D). See https://www.larousse.fr/dictionnaires/francais/prie-Dieu/63899
[Maybe in French with the “D”.]
I voted invariable, but I should prefer to have voted, “priez-Dieu.”
I should think the plural of “prie-dieu” would be “prayer desks”.
I don’t know about English, but in French, my mother tongue, as pAlban has noted, it is invariable. The reasoning is ”that object is used to pray the one God”; no matter how many of that object you have, there is only one God (and ”prie” doesn’t get an s since it is a verb). The same goes for ”timbre-poste” (post stamp) which becomes ”timbres-poste” in the plural form (”des timbres pour *la* poste”).
I’m not sure about many but two should be referred to as prie-dieu-dieu.
And, of course, the negative would be prie-deauxn’t
I would have pedantically voted for prions-dieu.
I’m grateful for this lighthearted post. Thank you.
The correct form of the plural is “prie-Dieu“.
It’s a grammatical exception, because you can’t put God in the plural (there is only one God).
Voted for the invariable because prie (a verb, to pray, so no ‘s’) and Dieu is God and as far as I know, there is only one God. :)
French Prie-Dieu are usually low upholstered chairs with a high back.
Whether it’s prie Dieu or prie Dieux, the pronunciation is the same
Moral: Keep it oral.
I should have said pries-dieu, but learn it’s prie-dieu in the plural. Any polytheism must be avoided, so it’s gins and tonic.
As a French person (and a former French teacher), I can certify that the plural is prie-Dieu (invariable). If anyone is interested (and experience teaches that most people aren’t), the rule for the plural of composite substantives in French is that any verbal element is invariable, whereas any nominal or adjectival element is inflected—except in the case of proper nouns.
As an aside, it seems the majority of voters on the question got it wrong. Winning the popular vote doesn’t mean much in some cases, I guess…
Why not use the (in small, but beautiful, parts of the world) established term Betbank? Though it may seem so, it has nothing to do with betting or gambling and even less with the Mammon or Wall Street. And it allows the use of the device for praying to the Saints or reading in Scripture, which may appear forbidden in French.
The proper plural is easy: Betbänke – no polytheism and no French …
Oh, please! Everyone knows the plural for a set of these is prie-two.
The Chicken
I voted electronically but also have 377 paper forms where I voted. Can I drop them off at your door tonight, sometime after midnight?
VP: Nah… I’ll just – you know – change the vote count. Keep the votes in case the wrong side catches up again.
This exercise reminds me of the zoo keeper’s mongoose/mongeese conundrum. (^__^)
Here is a prie-Dieu …. and over there we have four more.
(^__*)
Kneelers.
And if you want to say in French:
Kneelers in French…..
Too much time indoors?