建议信的英文是"letter of advice"或"advisory letter"。这个词的来源可能源于建议信中所包含的建议和忠告，以及信件这一形式。

一些英文例句和中文翻译如下：

I received a letter of advice from my lawyer regarding the contract. 我收到了律师关于合同的建议信。

The advisory letter from the bank warned me of the risks of investing in that company. 银行的建议信警告我投资那家公司的风险。

I wrote a letter of advice to my friend, telling her what to do in her current situation. 我给我的朋友写了一封建议信，告诉她目前的情况该怎么办。