Thickskulled is an adjective used to describe someone who is foolish or lacking in understanding. However, it is not always appropriate to use this word in certain situations. Therefore, here are some synonyms that can be used instead of thickskulled: dense, obtuse, dim-witted, insensitive, dull, unresponsive, blockheaded, and boneheaded. All these words connote a lack of intelligence or awareness. Thus, they can be used interchangeably with thickskulled in various contexts such as describing someone who is slow to understand a concept or idea. It is always advisable to choose the right synonym when using these words so as not to hurt anyone's feelings.