"Dependant upon" is a common phrase used to describe a relationship between two things where one relies on the other. If you are looking for synonyms, you can consider using "reliant on," "subject to," "contingent upon," "hinging on," "conditional on," or "determined by." These terms all convey a sense of dependence or reliance without repeating the same phrase over and over. Whether you are writing a formal document, an academic paper, or a piece of creative writing, using synonyms can add variety to your language and help you express your ideas more effectively.