Re:Why is a minute divided into 60 seconds, an hour into 60 ...
by nmc on Thursday January 16, 2014 @05:51AM
(#7068871)
This actually goes for beyond that!
70 is sixty-ten (soixante-dix), then 71 is sixty-eleven... and so on, up to 99: four-twenty-nineteen. Indeed, 80 is 4 times 20, hence "four-twenty" (quatre-vingt, without the "s" at the end).
Interestingly enough, French-speaking Belgians use the regular forms: 70 is "septante", 80 is "octante", and 90 is "nonante".
As for dix-huit and dix-neuf, the Romans counted down from twenty; duodeviginti (two-down-from-twenty) is eighteen and undeviginti (one-down-from-twenty).
So it probably made more sense to the early French to say dis-huit and dix-neuf instead.
But one interesting thing about French numbers that you have missed is that it possess a vestigial remnant of the vigesimal (base-20) number system of the Celtics, where 80 is quatre-vignts (four-twentys) to the French, and 90 is quatre-vignts-dix.