They've reduced the prices in the shop, so it's a good time to buy.
商店已經降低了商品的價格，看來現在是買東西的好時候。
2（與to連用）減少至
The fire reduced the forest to a few trees.
大火把森林燒得僅剩下幾顆樹。
This experienced editor is said to be able to reduce the misprints to almost nil.
據說這位經驗豐富的老編輯能把印刷錯誤幾乎降低到零。
3（與to連用）變為，化為
to reduce the rocks to dust
把石塊碎成粉末
4（與to連用）強迫；迫使
She was reduced to begging.
她被迫乞討。
5減肥
1 減輕嚴重性
Nothing could mitigate the cruelty with which she had treated him.
她對他太殘暴了，實在是罪無可恕。
The judge said that nothing could mitigate the cruelty with which the stepmother had treated the girl.
法官說沒有任何理由可以把那個繼母殘忍虐待女孩的罪責減輕。
2 緩和，減低（壞處、傷害等）
3 減輕（痛苦）
to mitigate the sufferings of the dying woman
盡可能減輕這垂死婦人的痛苦
如果非要區別的話，REDUCE是數量上的減少~MITIGATE是程度上的減輕~~~
以上我是摘取自現代漢英詞典的翻譯~