Crier au secours = To cry for help.

Secret

*Secret de deux, secret de Dieu,
Secret de trois, secret de tous = No secret but between two.

Seigneur

*À tout seigneur tout honneur = Honour to whom honour is due.

Sel

Mettre du sel sous la queue d’un oiseau = To put salt on a bird’s tail.

Sellette

Mettre sur la sellette = To cross-question; To haul over the coals (fam.).

[La sellette was the small wooden seat on which a culprit sat during his trial.]