The antonyms for the word "most undeviating" are varied and include inconsistent, erratic, unreliable, wavering, and fickle. These words highlight the opposite characteristics of what it means to be undeviating, which is to remain constant, steady, and firmly fixed. Being inconsistent means lacking a firm and unchanging course of action or behavior. Erratic refers to being unpredictable and irregular in one's actions, while unreliable suggests that one cannot be depended on consistently. Wavering suggests a lack of determination or certainty in one's actions, while fickle often implies a capricious or whimsical manner. All these words are the polar opposite of being undeviating, which is characterized by stability, steadfastness, and reliability.