loosener
/ˈluːsənə(r)/noun
1- a person or thing that loosens something使放松的人（或事）。
1.1
- informal a relatively undemanding challenge early in a game or competition, before the participants are fully settled or warmed up〈非正式〉（比赛中难度较低, 让选手热身的）开场题, 热身题。