1 the part of a gun that you press to fire it （枪的）扳机: to pull the trigger扣扳机
2 the cause of a particular reaction or event, especially a bad one 某种反应或事件的诱因（尤指不好的反应或事件）
trigger²
/ˈtrɪgə(r) ||; ˈtrɪgɚ/verb [T] trigger sth (off) to make sth happen suddenly 引发；导致: Her cigarette smoke had triggered off the fire alarm.她的香烟把火警警报器触响了。