The word "de-terminate" means to remove or cancel the determination or decision of something. Its antonyms are all the words that signify the act of making a decision or choice. Some of the commonly used antonyms include: determine, decide, conclude, settle, resolve, choose, elect, appoint, nominate, define, establish, and finalize. These words indicate the act of finalizing a decision or making a choice. The opposite of de-terminate is to bring an end to ambiguity, speculation or doubt by establishing a clear answer or solution. Using the appropriate antonym is crucial depending on the intended meaning. Therefore, it's essential to consider the context before using a word.