peripheral

peripheral
/-ərəl; -ərəl/ adj
1 ~ (to sth) of secondary or minor importance (to sth) 次要的; 不重要的
    topics peripheral to the main theme 围绕中心议题的小题目.
2 of or on a periphery 外围的; 边缘的
    peripheral zones 边缘地带.

牛津英汉双解词典