O liberty, how many crimes have been committed in thy name!自由啊！假你的名义犯了多少罪啊！

Oaks may fall when reeds stand the storm.树大招风.

Obedience¹ is the first duty of a soldier.服从是军人的第一职责.

Observation is the best teacher.观察为良师.

Of all the possessions of this life fame is the noblest; when the body has sunk into the dust the great name still lives.人生最可宝贵的是声誉，躯体入土后，声誉犹存.

Of earthly goods the best is a good wife. A bad the bitterest curse of human life.贤妻最可贵，恶妇是灾星.

Of nothing comes nothing.无中不能生有.

Of two evils choose the least.权衡两害，取其轻者.

Of young men die many, of old men escape not any.年轻人死得不少，而年迈者是在劫难逃.

Offence is the best defence.进攻是最好的防御.

Offense² is the best defense³.进攻是最好的防御。

Often and little eating makes a man fat.少吃多餐，身强体胖.

Old bees yield no honey.老蜂不酿蜜.

Old birds are not caught with new nests.新巢捉不到老鸟.

Old birds are not to be caught with shaff.老谋是不会失算的.

Old foxes want no tutors.老狐狸不需要教师.

Old friends and old wine are best.古交友情深，陈酒香味醇.

Old friends and old wines are best.陈酒味醇，老友情深。

Old love will not be forgotten.旧情永难忘.

Old sin makes new shame.一失足成千古恨。

Old vessels⁴ must leak.旧船必漏.

Old wood best to burn, old wine to drink, old friends to trust, and old authors to read.老柴最好烧，陈酒最好饮，老友最可靠，老作家的书最好读.

Old wood is best to burn, old book to read.老柴好烧，老书宜读.

Old wood is best to burn, old horse to ride.老柴好烧，老马好骑.

Older and wiser.越老越聪明.

Omelets are not made without breaking eggs.有失才有得.

On the choice of friends. Our good or evil name depends.朋友的选择可影响名誉的好坏.

On the great clock of time there is but one word, "Now."在伟大的时钟上，只有一个词，就是“现在”.