Least​

Least is an adjective that means the smallest amount:

Least是一个形容词，意思是“最小得;最少得(little得很可以)”。

We need the least amount of friction possible.

我们需要尽专家少得摩擦。

Lest

Lest is a conjunction that refers to averting or circumventing something

Lest则是一个连词，表示“回避或回避某事;唯恐，以免，只怕”

Memorial Day is a holiday to reflect on past wars lest we forget the soldiers who fought for our freedoms.

烈士纪念日是一个缅怀过去战争得节日，以免我们忘记那些为我们得自由而战得战士。

At Least

至少，起码

The English expression at least can be used before/with a verb, signifying that something can be done despite circumstances, or before/with a number/quantity, signifying a minimal quantity.

在英语表达中通常用在动词前或者动词连用，表示不管情况如何都专业做某事;用在数量前，表示最小值

Although ill, at least I am here.

虽然我生病了，至少我还在这儿。

I wish to buy at least three presents.

我希望我能买至少3个礼物。

最后我们来总结一下

least是一个形容词，

意思是“最小得;最少得”，也就是little得很可以

lest则是连词，

“唯恐，以免”得意思

他们两个只是长的像而已

而“至少”则是at least