Marginal有2个很常见的意思.
small and not important 小的;微不足道的;不重要的
a marginal improvement in weather conditions 天气条件的略微好转
The story will only be of marginal interest to our readers. 我们的读者对这则故事不会很感兴趣。

not part of a main or important group or situation 非主体的;边缘的
marginal groups in society 社会中的非主流群体

hillside就是小山坡的意思.
Our hotel was on the hillside overlooking the lake.
我们的旅馆位于可俯瞰湖水的小山坡上.

Rainfall就是降雨量的意思.
There has been below average rainfall this month.
这个月的降雨低于平均降雨量.

In any case的意思就是: whatever happens or may have happened 无论如何;不管怎样
There's no point complaining now─we're leaving tomorrow in any case.
现在抱怨毫无意义,反正我们明天就要离开了.

Either way, it is important to establish good ground cover to avoid the loss of soil through erosion.
either way; one way or the other
used to say that it does not matter which one of two possibilities happens, is chosen or is true两者都一样
Was it his fault or not? Either way, an explanation is due.
是他的错不是?无论是不是,都得有个解释.
We could meet today or tomorrow─I don't mind one way or the other.
我们可以在今天或明天见面,哪一天对我都行.

Erosion就是侵蚀,腐蚀的意思.
Soil erosion by rain and wind is a serious problem here.
雨和风对土壤的侵蚀在这儿是个严重问题.

动词的形式是erode,那么这个单词的本意就是" 侵蚀;腐蚀;风化".
The cliff face has been steadily eroded by the sea.
峭壁表面逐渐被海水侵蚀.
The rocks have eroded away over time.
这些岩石随着时间的推移逐渐风化了.

还有一个引申义: to gradually destroy sth or make it weaker over a period of time; to be destroyed or made weaker in this way 逐渐毁坏;削弱;损害 written often passive ~ (sth) (away)
Her confidence has been slowly eroded by repeated failures. 她的自信心因屡屡失败慢慢消磨掉了.
Mortgage payments have been eroded(= decreased in value)by inflation. 偿还的按揭贷款因通货膨胀而降值.