When someone "caves in to" another person, it means they have given in to that person's demands or pressures. Some antonyms for this phrase could be standing firm, holding out, resisting, or standing one's ground. These words convey the opposite meaning of "caving in" and suggest a stance of firmness and determination. In some situations, it may be necessary to compromise or find a middle ground, but in others, it is crucial to be unwavering in one's beliefs and values. Using antonyms for "caves in to" can help to express a sense of strength and conviction in one's actions and decisions.