信的英语单词是letter. 比如一封有100字的信翻译成英语就是：A 100 words letter或者 A letter with 100 words.
【下面给你一些与信有关的短语】： 回信：letter in reply;to write back 宠信：to favor and trust 潮信：tides 拆信：to open a letter 坚信：to believe firmly 失信：to break one's promise 确信：to make sure;to believe firmly 轻信：to believe readily 亲信：confidant 平信：ordinary letter;surface mail
【双语例句】： 收到你的信，我当时就回了信。 I wrote back to you immediately after I received your letter. 读了她的信，我的心情久久不能平静。 I couldn’t calm myself down long after I read her letter. 我坐起身来，一鼓作气写完了给她的信。 I sat up and finished my letter to her in a determined burst of energy. 我近日没有收到他的信。 I haven’t heard from him recently/lately. 我们几年前曾经通过信。 We corresponded a few years ago.
