sine qua non/ˌsɪneɪ kwɑ: ˈnəun; `sɪnɪ kwɑ `non/ (fml 文) essential condition; thing that is absolutely necessary 必要条件; 必不可少的事物 Patience is a sine qua non for a good teacher. 做个优秀教师必不可少的条件是要有耐心.
牛津英汉双解词典