小三儿怎么说的？
Mistress
Mistress是比较正式的表示“情妇”的用法，这个词比较有历史感，路易十五的情妇Madame de Pompadour还以智慧和风情著称。现在多用来指婚外情，“a woman who has an ongoing extramarital sexual relationship with a man”。
例句：
Genji, when still very young, has a passionate affair with his father's mistress. （New Yorker）
源氏年轻时和父亲的情妇爱得不可自拔。
Former U.S. military commander and CIA director David Petraeus will appear in federal court in North Carolina on Thursday to face sentencing for allegedly leaking secrets to a mistress who was writing his biography. （AP）
美国前指挥官、CIA主任David Petraeus周四在北卡罗来纳联邦法庭受审，面临向为其写传记的情妇泄露机密的指控。
Liu Tienan, a former top Chinese economic planning official, was convicted of bribery and jailed for life after his mistress gaving incriminating information to a journalist who posted online her accusations of shady business deals, fack academic credentials and death threats. （Xinhua）
中国发改委前官员刘铁男被控受贿并判无期徒刑，此前其情妇向记者泄密，后者将之发布在网上，指控其涉嫌不法交易、学历造假并对其进行死亡威胁。
Paramour
The noun paramour evolved from the French phrase par amour, meaning “passionately” or “with desire.” If you break it down, you getpar, meaning "by," and amour, the French word for love. Once upon a time, women used this word to describe Christ, and men would use it to refer to the Virgin Mary. But eventually, paramour shed its religious connotations and came to mean “darling” or “sweetheart,” and later “mistress” or “clandestine lover.”
paramour来自法语，by love的意思，曾经被女性用来表示基督，男性用起表示圣玛丽，后来失去了宗教指涉，变成了“小甜心”，最后还有了“小三儿”、“傍尖儿”的意思。相比于mistress，这个词比较温和，更强调婚外情中“情”的那个方面，也用来表示“情夫”。
例句：
The authorities were apparently planning to transfer his paramour to another correctional facility.
当局显然计划把他的情妇转到另一个劳教机构中去。
kept woman
An adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man. DailyMail还写过一篇挺不符合社会主义精神文明要求的书评，当然是从幽默的角度说的。
例句：
She has never seen the film, but knows that presenting becoming a kept woman as a viable career option is a risqué (伤风败俗的) business. （Washington Post）
她没看过这部电影，可她知道把给人做小三当成一种人生选项是伤风败俗的事。
To Mainlanders, Hong Kong felt like a kept woman, one upon whom material comfort is bestowed at the cost of compromised dignity. （New Yorker）
大陆人眼里，香港就像小三儿，吃我们的喝我们的，没什么尊严。
fancy woman
和Kept woman一样，fancy woman可以更准确的翻译为“被包养的人”，通常有道德水准存疑的色彩。可fancy man的意思略有不同，fancy man可以指“情夫”，也可以泛泛地用来说“帅哥”，甚至“同人”。fancy woman和fancy man的不同感情色彩也暗示了性别不平等存在于语言深处。
doxy
doxy可以用来简称orthodoxy(宗教教条)，可更多情况下有着完全相反的用法，“小蜜”、“小狐狸”，差不多就是这个意思，没有mistress那么正式，有丰富的感情色彩。
courtesan
From the Renaissance on, European kings and noblemen often kept acourtesan, that is, a women with whom they had a relationship but were not married to.
和concubine一样，courtesan是个“古香古色”的词，因为住在宫廷，所以和court看起来很像，实际上，随着民主化的发展，这种职业正在式微，但也并未消失，郭美美可能算比较典型的courtesan，主要是生意，无关感情。
例句；
Dutch exotic dancer, courtesan, and accused spy who was executed by firingsquad in France for espionage for Germany during World War I.
她生前曾是一名荷兰脱衣舞娘、情妇、间谍，最终因在一战期间为德国做间谍而被法国行刑队处死。
concubine
实际上，用concubine表示“小三儿”是不确切的，更准确地说，concubine是“小妾”或“妃子”，杨贵妃和甄嬛都曾是concubine，这没什么拿不上台面的，制度使然。在这个意义上，concubine本身不承担道德义务，倒是某种前现代制度的牺牲品。
例句：
The Islamic State vowed to kill all the men and make concubines of the women. （Washington Post）
伊斯兰国号称要杀死所有男人，让女人为妾。
Persian King Darius III also had several wives and kept a stock of 360 royal concubines “for his own personal use.”
波斯国王大流士三世有数个妻子，和360个妃子供自己享乐。
home wrecker
One who comes into your life, and screws it all up. This involves stealing your boyfriend/girlfriend, puppy, your friends, until they pretty much take over your entire life.
抢走你男人的女人。
That home wrecker stole my man!!
I am Jackie, you are Marilyn
我是正房，你是小三儿。
这个说法有点意思，Marilyn招谁惹谁了，怎么就小三儿了呢。这背后有个典故，Jackie是美国前总统肯尼迪的夫人Jacqueline Kennedy，聪明又优雅；不说也知道了，Marilyn就是Marilyn Monroe，甜美诱人的梦露，梦露就是传言中肯尼迪的小三儿，于是Jackie和Marilyn的形象也刻板化为正房和小三儿了。不少美国的Quiz还测试女孩子适合当Jackie还是是Marilyn。
hanky-panky
本意是偷鸡摸狗的小伎俩，引申为不合法的两性关系，也用来泛指男女间卿卿我我的事。
play the field
脚踩两只船，玩弄别人感情。可能这不违法，但没道德，如果是党员，还破坏了党的规矩。一个脚踩两只船的人怎么说？Two-timer。
She's not interested in marriage at this stage, so she's quite happy to play the field.
Fling
短期的同居关系，比一夜情要长，又没有婚外情那么严肃。
It was just a fling with David... I don't expect it to go into a relationship.
fornication
很正式的词，表示通奸。
The policy also mandated disciplinary action for sexual assault, incest, adultery and fornication. （Reuters）