1.diminish的基本意思是“减少”“缩小”,指某事物对照原本基础上数量或质量少了很多; 常引申表示“减弱…的权势”。
2.diminish可用作不及物动词,也可用作及物动词,作及物动词时,其后多接名词或代词作宾语。

diminish by (v.+prep.)
由于…而减少 reduce for (some reason)
▲diminish sth by sth
Diminish the revenue by reducing tax.由于减税而使这个国家的税收减少。

用作不及物动词
▲S+～(+A)
The campers's food supply gradually diminished as the days were on.随着一天天地过去,野营人的食物逐渐减少了。
The cost of the production greatly diminished.生产成本大大地减少了。
用作及物动词
▲S+～+n./pron.
The long war greatly diminished the country's wealth.长期的战争使这个国家的财富锐减。
Unforeseen expenses diminished his savings.意外的支出减少了他的存款数目。
We should try to diminish the cost of production.我们应尽力减少生产成本。
Several unpopular decisions diminished the governor's popularity.几项不得人心的决定使州长的声望下降。

diminish, decrease, lessen, reduce
参见reduce条。