"hypostasis" means the fundamental or essential nature of something. It refers to the underlying substance or essence that makes something what it truly is. Full definition
The multi-layered hypostasis of Johnson's works combines a crude confrontational intervention on a personal and inter-personal level in dialogue with aspects of social significance. (theseenjournal.org)
They, therefore, rejected the Chalcedonian view that there was only one hypostasis in Jesus. (religion-online.org)
The Greek word hypostasis translated «substance» here can mean various things, including hope, confidence, or promise, so the first part of the statement might be saying only that faith is a kind of confidence in what we hope for. (faith.org.uk)