to reduce the rate at which money can be exchanged for foreign money

Last year Mexico was forced to devalue the peso. 去年墨西哥被迫将比绍贬值。

to cause someone or something to be considered less valuable or important

I don't want to devalue his achievement, but he managed to get a promotion without working very hard. 我不想贬低他的成绩，但他似乎没有真正努力就得到了升迁。