Synonyms for Substantive (same or very similar meaning)
WordNet sense 1 (being on topic and prompting thought):
meatyWordNet sense 2 (having a meaning or purpose):
meaningfulWordNet sense 3 (having a firm basis in reality and being therefore important, meaningful, or considerable):
substantialWordNet sense 4 (basic and fundamental):
essentialFrom the ODE community, based on WordNetadd/edit