There are many synonyms for the phrase "of substance". Some examples include "significant", "important", "meaningful", "substantial", "essential", "weighty", and "crucial". When describing something as "of substance", it suggests that it has a certain level of importance or relevance. This could refer to a topic of discussion, an argument, a point made, a decision, or a piece of information. Whatever the context, using synonyms for "of substance" can add depth and significance to the language used, conveying a sense of gravity and impact. The appropriate choice of synonym can help to emphasize the importance of what is being conveyed.