dunderhead

donder-, 拟声词，打雷，雷声。比较thunder, blunderbuss. 引申义被雷劈傻的。

dunderhead (n.)

1620s, from head (n.); the first element is obscure; perhaps from Middle Dutch doner, donder "to thunder" (compare blunderbuss).

1. these words are used to express a low opinion of someone's intelligence