Consider terminus the end of the line. Whether it describes a train station, a goal, or an era — terminus refers to something’s final point.
Ancient Romans worshiped Terminus as the god of boundaries, even performing sacrifices in his honor to bless objects that marked borders. You probably don’t have to go that far if you just want to use the noun terminus. You can use it as a weighty way to indicate something is at the end of the line, such as the last stop on a bus or train route. It most often refers to the end of a transportation route, but it can also be used more generally to mark the end point of other things — such as a marriage or a project.