Nothing is so necessary for travelers as languages.
Nothing is to be got without pains but poverty.
Not to advance is to go back.
Not to know what happened before one was born is always to be a child.
No way is impossible to courage.
Obedience is the first duty of a soldier.
Observation is the best teacher.
Offense is the best defense.
Old friends and old wines are best.
Old sin makes new shame.
Once a man and twice a child.
Once a thief, always a thief.
Once bitten, twice shy.
One boy is a boy, two boys half a boy, three boys no boy.
One cannot put back the clock.
One eyewitness is better than ten hearsays.
One false move may lose the game.
One good turn deserves another.
One hour today is worth two tomorrow.
One man's fault is other man's lesson.
One never loses anything by politeness.
One swallow does not make a summer.
One's words reflect one's thinking.
Out of debt, out of danger.
Out of office, out of danger.