辜负的英文：
let down
fail to live up to
disappoint
betray
fall short of
be ungrateful to
wrong
be unworthy of
disappoint

参考例句：

He doesn't give two hoots for all your weeping and wailing and gnashing of teeth!"
辜负了你的长太息而痛哭流涕！”

to betray a trust
辜负所托

To be insensible to kindness
辜负恩德

Don't betray the trust of the people.
不要辜负了人民的信任。

A breach of trust
违反信托,辜负信任

We should justify the ardent expectations of our teachers.
我们要不辜负老师的殷切期望。

I will not abuse your hospitality.
我不愿辜负你的招待。

He did not come short of the expectations of his parents.
他没有辜负父母的期望。

He was filled with guilt at having failed his parents.
他因辜负了父母亲而内心深感不安。

He could not abuse their trust.
他不能辜负他们的信赖。

let是什么意思：
v. 允许；让；假设；出租
n. 擦网球

Let it be as you desire.
就按照你的意思办吧。

Let in sheathing.
镶进夹衬板。

He let go of the pole and let it fall.
他松开那根柱子，让它倒下了。

down是什么意思：
prep. 在…下，沿着
v. 下降，打倒
n. 潦倒；羽绒；丘陵

Down with hegemonism!
打倒霸权主义！

The sun is down.
太阳下山了。

Close down autos and you close down steel and rubber.
关掉了汽车工业你也就关掉了钢铁工业和橡胶工业。

fail是什么意思：
n. 不及格
v. 失败，不及格；破产；缺乏；衰退

If you fail to plan, you plan to fail.
如果你不做计划，那就是在计划着失败。

The download failed.
下载失败。

Intelligent as you are, I suspect you will fail.
尽管你聪明，我还是猜想你会失败。