"Thickwit" is a derogatory term used to describe someone who is considered to be unintelligent or slow-witted. There are several synonyms that can be used to describe such a person including "dullard," "simpleton," "blockhead," "dunderhead," "dolt," "nincompoop," "idiot," "moron," "imbecile," or "dimwit." These words may differ in the degree of insult they convey or the context in which they are used, but they all refer to someone who lacks intellectual acuity or common sense. It's important to use language wisely, as name-calling and insults can damage relationships and cause harm both to the speaker and the person being insulted.