Definition Significant and substantial are two words that are often used interchangeably, but they actually have distinct meanings. Significant typically refers to something that is important, meaningful, or noteworthy. It implies that the subject in question has a considerable impact or influence. On the other hand, substantial usually refers to something that is large in size, amount, or extent. It suggests that the subject is considerable or significant in a physical sense. Impact When ... Substantial means considerable in importance, value, degree, amount, or extent. It also means solidly built, strong, ample, or real. Find synonyms, antonyms, and examples of substantial in different contexts. Discover the meaning of substantial , what substantial means, and how to use substantial correctly. Complete guide with definitions, examples, and usage tips. Substantial definition : Considerable in importance, value, degree, amount, or extent.