The word "in-substantialities" refers to things that are lacking in substance, weight or importance. Antonyms for this word would be terms that represent concepts, ideas or objects that are concrete, significant, and meaningful. These antonyms might include words like "substance," "weightiness," "importance," "significance," or "value." In contrast to in-substantialities, they describe something that has tangible or discernible qualities, that holds significance or weight in a particular context, or has a critical role in a given situation. These antonyms are useful in describing things that exist in the world and hold genuine importance to us, in contrast to things that are merely fleeting or insubstantial.