What are the opposite words for in substantial?

The antonyms for the word "in substantial" are "insignificant," "inconsequential," "trivial," "unimportant," "negligible," and "minor." These words describe something that is not significant or of little consequence. If something is "insignificant," it is not important or meaningful. "Inconsequential" refers to something that has no real impact or influence on a situation. "Trivial" means something that is of little importance or worth. "Unimportant" refers to something that is not essential or necessary. "Negligible" describes something that is so small or insignificant that it can be disregarded. Lastly, "minor" refers to something that is not significant or major.