If you say 某人积怨甚广，then you are saying that a lot of people hold grudge or hatred against this person, and this person has many enemies.

这是文言词，也可以是成语。甚:在中国古代有很的意思，就是积怨很广，从字面单个意思叠加即是意思

这是个简称，你可以把他一个字一个字地看 积（积累） 怨（怨恨） 甚（很；在中国古文中也有 多 的意思） 广（广大，宽泛） 也可以简单地理解为 ：有很多的怨恨 哈哈哈中国人很少说这个词，因为这种词听起来很专业

Accumulated, complains, pretty much, everywhere. This is roughly what every character in this idiom means. You could translate it as follows: the accumulated complains about the person mentioned in the context is pretty much everywhere.

A person has bad relationships with many people in a social circle, no one likes him/her in terms of the person's bad behaviors in the past.