central
Located in the middle or most important part of something.
Central means located in or forming the center of something, or being most important. The central part of a city is its downtown core, where major buildings and activity cluster together. Your school's central hallway might be the main corridor where all the other hallways connect.
When something is central, it's often the key piece that everything else relates to. In a story, the central character is the main person the plot revolves around. The central idea of an essay is its most important point, the one everything else supports. A team's central player might be the person everyone depends on most.
A bicycle wheel has a central hub where all the spokes meet. Your brain's central nervous system coordinates your whole body. When someone says an issue is central to a discussion, they mean it's the most important topic, not a side detail.
Notice that central suggests both position and significance: things at the center tend to matter most because everything connects to them.