Don't rely on us French folks to elucidate either, we also say quinze jours (15 days) for two weeks - it's very odd. Usually, it’s when people are talking about going on vacation. People work all day on the Friday, so it doesn’t make sense to count that day.

Mind you, we also call a quarter (a 25-cent coin) a “trente-sous” which means thirty cents, so I’ll just walk away in embarrassment now.

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TEd, does the bible say whether Jesus died in the morning? Maybe that’s why they say it is three days. If he died at night, then I’d definitely say two days later, not three.