emission
/ɪˈmɪʃn; ɪ`mɪʃən/ n
1 [U] (fml 文) sending out or giving off (of light, heat, fumes, matter, fluid from the body, etc) （光、 热、 烟、 气、 分泌物、 体液等的）散发, 发射, 发出
the emission of light from the sun 阳光的照射.
2 [C] thing that is sent out or given off; discharge 散发之物、 发出之物; 流出物; 排泄物
a nocturnal emission, ie the discharge of semen during sleep 夜间遗精.