Antonyms for the word "anti thetical" include words such as corroborative, complementary, harmonious, compatible, and supportive. These words are used to describe things that work together or support each other, as opposed to being in opposition or contradiction with each other. The opposite of something that is anti thetical is something that is in agreement with or reinforces something else. For example, a statement that is corroborative supports or confirms a previously made statement, whereas something that is anti thetical contradicts it. By understanding the antonyms for anti thetical, one can better understand the nuances of language and meaning in different contexts.