> The final "s" is usually silent in French and I'm not aware of any rule for what defines the exceptions. I don't think there is a rule. The 19th-century book

> The final "s" is usually silent in French and I'm not aware of any rule for what defines the exceptions. I don't think there is a rule. The 19th-century book said this: >> L's s'est maintenu ou définitivement rétabli depuis plus ou moins longtemps dans maïs, jadis, fi(l)s et lis (y compris fleur de lis le plus souvent, malgré l'Académie); dans metis, cassis, vis (substantif) et tournevis. La prononciation de ces mots sans s est tout à fait surannée; on ne peut plus la conserver que pour les nécessités de la rime, et encore! The reference to /s/ being maintained or reestablished, and the pronunciation without /s/ being out of date, suggests to me that the rule was that final /s/ was lost (in Parisian French, I guess...), and that there was a specific effort to put it back into some words. But that's speculation on my part. It seems clear that bus "bus" and maïs "maize" have a final /s/ because they are foreign words. It's less clear to me why they're given those spellings as opposed to something more like busse.