这两个形容词均含有“荒谬的”之意。absurd 普通用词，强调指违背常理的荒谬。ridiculous强调荒谬到令人发笑的地步。比较：
No doubt it is very absurd. 毫无疑问这是很荒谬的。
It’s absurd to be afraid of them. 害怕他们是荒谬的。
It’s absurd to make any such claim. 提出任何这样的要求都是荒谬的。
To maintain that we can survive a nuclear war is absurd. 认为我们能在核战争中幸存下来的说法是荒唐的。
This is perfectly ridiculous. 这非常荒谬可笑。
Whoever told you such a ridiculous story? 这荒谬的故事是谁给你讲的?
It is ridiculous that we should be ( = that we are) short of water in a country where it is always raining. 在经常下雨的国家里我们竟然会缺水，这简直是荒谬。
So ridiculous did she look that everybody burst out laughing. 她的模样如此滑稽，大家都捧腹大笑。
It’s ridiculous to sing songs that you don’t know what they mean. 唱歌却不知道歌词的意思是很可笑的。