The term "substantialness" indicates that something is substantial or significant in size or quality, possessing importance or weight. Some of its antonyms, which indicate the opposite meaning, would be triviality, insignificance, smallness, slightness, or inconsequence. These words suggest a lack of importance, weight, or value of something. Conversely, some of its synonyms, which indicate a similar meaning, would be substance, significance, importance, weightiness, or heft. These words suggest that whatever is being described possesses noteworthy attributes, characteristics, or qualities that set it apart and make it distinctive. By using antonyms and synonyms, a writer can create a more vivid picture in the mind of the reader, making the written text more compelling and engaging.