sub rosa (L.). Under the rose, privately.
sub voce (L.). Under such or such a word.
sui generis (L.). Of its own peculiar kind.
summum bonum (L.). The chief good.
suum cuique (L.). Let everyone have his own; honor to whom honor is due.
Tant mieux; tant pis (Fr.). So much the better; so much the worse.
tempora mutantur, nos et mutamur in illis (L.). Times change, and we with them.
tempus fugit (L.). Time flies.
tenax propositi (L.). Tenacious of purpose.
terra firma (L.). Solid earth.