The adjective contingent can be used to describe something that can occur only when something else happens first. Making money is contingent on finding a good-paying job.
When an event or situation is contingent, it means that it depends on some other event or fact. For example, sometimes buying a new house has to be contingent upon someone else buying your old house first. That way you don't end up owning two houses! As a noun, contingent means either "a group of soldiers that joins a larger force," like a contingent of British troops sent to assist American soldiers, or "a group of people with something in common," like the contingent of folks dressed as Batman at Comic-Con.