匿名信的英文：
an anonymous letter

参考例句：

It is an anonymous letter.
这是一封匿名信。

Three day after Rastus' disappearance, Mrs. Ramsay received an anonymous letter.
拉姆斯特斯失踪3天后，拉姆斯齐太太收到一封匿名信

anonymous是什么意思：
adj. 匿名的；无名的；没特色的

Of course, that would have to be by anonymous vote.
当然，那必须通过不记名投票的方式。

The writer wishes to remain anonymous.
作者希望姓名不公开。

An anonymous donor,buyer,benefactor,etc
不透露姓名的捐赠者,购买者,捐助者等

An anonymous well-wisher bailed the prisoners out.
一个不留姓名的好心人把那些在押犯保释出来了。

His car was an anonymous-looking Ford.
他的车是一辆没有明显特征的福特牌。

letter是什么意思：
n. 字母；信；字面意义；证书，许可证；文学
v. 用字母标明，写字母于；写印刷体字母；赢得校名缩写字母标志

in letter and in spirit
在字面意义和精神实质上|无论形式和实际

The letter was a forgery.
这封信是伪造的。

Post the letter through the slit in the letter box.
把这封信从信箱的投信口投进去。

Imprint a postmark on a letter =imprint a letter with a postmark
盖邮戳于信上

The letter is directed to him.
这封信是写给他的。