The antonyms for the word "be undetermined" are numerous and varied. One antonym could be "be determined," indicating a clear and unwavering decision or course of action. Another antonym might be "be resolved," suggesting that a particular issue or question has been fully and conclusively settled. Other antonyms might include "be decisive," "be certain," or "be definitive," each indicating a strong and definitive sense of purpose or direction. In contrast to "be undetermined," these antonyms all suggest a clear and definite sense of direction, purpose, or resolution, providing a useful contrast and variety of meanings in the English language.