The term "extremistic" refers to someone or something that holds extreme beliefs, views, or opinions. However, there are many synonyms that can be used instead of "extremistic," such as radical, fanatical, fundamentalist, militant, aggressive, and extremist. These words imply a strong belief system that often leads to a willingness to use violence or extreme measures to achieve their goals. Some other synonyms that can be used include zealous, fervent, and intense. It's important to note that these words can also have negative connotations, as they often refer to people or groups with extreme views that may cause harm to others.