focal
/ˈfəʊkəl/adjective
1- of or relating to the centre or main point of interest（与）焦点（有关）的; 最关注的; 主要的：
the focal symbol of sovereignty is the crown.
君主的主要象征是王冠。
1.1
- Optics of or relating to the focus of a lens【光学】（与）透镜焦点（有关）的。
1.2
- (of a disease or medical condition) occurring in one particular site in the body（疾病, 病状）病灶的, 灶的。
词源
late 17th cent.: from modern Latin focalis, from Latin focus, or directly from FOCUS.