That is not performing or being performed; (now) esp. not functioning well or to the expected standard; (Finance) = non-performing, adj. 3.
(un-, prefix1 affix 4.)
英语词典包含1132095条英英释义在线翻译词条，基本涵盖了全部常用单词的英英翻译及用法，是英语学习的有利工具。