The distinction between substantial and significant as adjectives is that substantial is having substance; genuinely being; real; as in substantial life, and significant is indicating something; bearing significance. A signature can be significant without being substantial. Signatures are usually only a few lines long, so they cannot provide much insight into the writer's personality. Something substantial is worth considering because it has great importance or value. Your comments are very helpful and will help me to improve my writing skills. Your email address will not be published and is used solely for contacting you regarding your request. Thank you. Significant means having an influence or being relevant; having a direct relation; having something that is significant. Something significant is worth paying attention to; can have an impact on you. The movie played at midnight had a significant effect on many people. His death was considered a significant loss to American cinema. In mathematics, significant numbers are those that cause changes when added or subtracted from other numbers. For example, if 5 were found to be a significant number, then adding it to or subtracting it from other numbers would produce different results each time.