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I have seen on Facebook, a post (in French) claiming that many words for the night are based on a n+respective number for the number 8. For example on this website,

Language Number 8 night
français huit nuit 
anglais eight night 
allemand acht nacht
espagnol ocho noche 
portugais oito noite
italien otto notte
néerlandais acht nacht
suédois aetta natta 
roumain opt noapte
wallon ût nut 
occitan uèch nuèch 
catalan vuit nit 
gascon ueit nueit 
picard uit nuit 
piedmontais eut neuit 
espéranto ok nokto

The post goes even further, claiming that N is a symbol for infinity, and that 8 is the typical infinity symbol rotated.

My first reaction was to dismiss it. But then, I've been thinking about it, and would really like to have reasons to dismiss it.

The infinity symbol dates from 1655 (according to Wikipedia)whereas the word nuit was already in use by 1170 (website in French). Furthermore, the word nuit was used as noit in older French, and derives from noctum (latin) and thus nox (littré in French). But unfortunately, my knowledge of Latin is by far too limited to investigate further on the Latin.

Actually, the last link mentions that for the author M. Ad. Regnier, studying the Sanskrit, it could be related to the word naked (German: nackt, Latin: nuda).

In English, (the ight deriving from eight sounds worse than some other examples), what I gather is that

Old English niht (West Saxon neaht, Anglian næht, neht) "night, darkness [...] from Proto-Germanic *nahts

which relate as well to nox (Latin), nuks (Old Greek) or naktam (Sanskrit). The same website also indicates that

according to Watkins, probably from a verbal root *neg- "to be dark, be night."

But, if the relation night -> infinity -> infinity symbol -> 8 -> night, sounds improbable, I cannot find definitive information on a possible relation between the number 8 and the night.

Can you help me get down to the bottom of that question?

No, they are unrelated.

Some Proto-Indo-European language (PIE) reconstructions from Wiktionary:

• "eight": "oḱtṓw" (claimed to be a dual of "four fingers")


• "night": "nókʷts" (possibly from "bare, naked")

As @Schmuddi mentioned in a comment above, it looks just like a coincidence (slightly similar proto-language words). The rest looks like an urban legend.

In English "eight" and "night" came from different words, "ehte" and "niht" respectively, which have both undergone a common substitution of -gh- for a hard "h", which was a Middle English scribal habit.

In French, "huit" came from "uit" when an "h" was added to avoid confusion with "vit". As for "nuit", it's a transformation of old French "nuict" derived from latin "noctem", which is an inclination of "nox".

The etymological link can be tracked further down, but the two words remain distinct, albeit similar.

So at least for English and French, the similarity between these two words is not due to a common root, but rather to similar ancestor words, and in some cases common transformations which contributed to the similarity of modern forms. I don't know other languages in your list, but they all seem to be either Latin or Germanic, so they likely share their etymological transformation with French and English respectively.

To pile on the answers debunking a particular language:
The list misspells both Swedish words to make them look more similar than they are. "Åtta" (number eight) is misspelled as "aetta" and "natt" (night) is misspelled as "natta".

"Åtta" /ˈɔtːa/ and "natt" /nat:/ are not very alike as I'm sure most will agree.

Count this as another vote for occam's razor and this being an urban legend.

(Source: My Swedish dictionary. Wiktionary unfortunately is short on IPA for these but consider it "common knowledge"...)

Roberts French dictionary says that nuit (night) comes from the Latin noctis meaning nocturnal (vient du latin nox, noctis → noctambule, nocturne).