Si
Il n’y a pas de si qui fasse = There is no excuse for it.
Avec un si on mettrait Paris dans une bouteille = Such suppositions are idle; If wishes were horses, beggars would ride.
Il n’est pas riche.—Oh! que si = He is not rich.—Isn’t he, though!
Sien
*Chacun le sien n’est pas trop = Let each have his own, then all is fair.
Il fait des siennes = He is up to his old tricks again.
Il en sera du sien = He will be a loser by it.
On n’est jamais trahi que par les siens = It is always one’s friends (or, confederates) who betray one.
Singe