The term "making a dent" typically denotes having a significant impact or influence on something. To express the opposite meaning, one can use antonyms such as "ineffective," "insignificant," or "negligible." Instead of making a dent, one could say that their actions had no impact or did not leave a mark. Similarly, if something is unlikely to make a difference, it can be described as inconsequential, trivial, or unimportant. Moreover, if someone or something has no effect whatsoever, they can be deemed irrelevant or immaterial. Thus, antonyms for "making a dent" can help convey a range of opposing ideas, from slightness to complete ineffectiveness.