A cad is a man who will not do the decent thing, especially toward women: he lies, he uses people, he walks away when someone needs him.

A cad is a man who will not do the decent thingcad 是指不肯做正派事的男人， especially toward women尤其是對女性： he lies, he uses people, he walks away when someone needs him他說謊、利用別人，別人需要他的時候他就閃人。

The word feels old — like a black-and-white film, or a novel where people still say “sir.” Young people almost never call someone a cad in ordinary talk; they might say it with a small smile, as if putting on a costume. It is an insult, but a rather polished-looking one, which is part of its flavour.

The word feels old這個字聽起來很老派， like a black-and-white film, or a novel where people still say "sir."像黑白電影，或是小說裡人還在說「sir」的年代。 Young people almost never call someone a cad in ordinary talk年輕人平常幾乎不會叫人 cad， they might say it with a small smile, as if putting on a costume就算說了，也可能是帶著一點笑意，像在扮裝一樣。 It is an insult, but a rather polished-looking one這是罵人的話，但看起來還蠻體面的， which is part of its flavour這也是這個字味道的一部分。

It started as a short form of caddie, and further back it ties to French cadet (a younger son, a junior). Over time the “junior fellow / odd-job man” sense picked up a moral stain and became “a man you cannot trust.” You will still meet it in period stories.

It started as a short form of caddie它原本是 caddie 的簡短說法， and further back it ties to French cadet (a younger son, a junior)再往前追，跟法文 cadet（次子、晚輩）有關。 Over time the "junior fellow / odd-job man" sense picked up a moral stain後來「小弟／打雜的人」這個意思沾上了道德上的污點， and became "a man you cannot trust."變成「不能信任的男人」。 You will still meet it in period stories你還是會在時代小說裡遇到它。

In the street today, English has blunter words.

In the street today現在在街頭上， English has blunter words英文有更直接的說法。