Being undecided refers to a state of indecisiveness or uncertainty, where a person cannot make a definitive choice or decision. The antonyms for the word "being undecided" include being determined, decisive, certain, resolute, and confident. Choosing one of these antonyms depends on the context of the situation, and the personality of the individual making the decision. Being determined refers to someone who is emotionally invested in a choice and is willing to take proactive measures to achieve it. Decisive means making a clear, firm, and quick decision with no delay or wavering. Being certain means having no doubt in one's mind or being sure of a decision. Resolute means having a strong will and being unshakeable in one's decision or path. Lastly, being confident refers to having complete trust in oneself and one's choices.