let/set/turn (someone or something) loose : to allow (someone or something) to move or go freely放任；使自由活动
He let/set the dogs loose in the courtyard.
他让狗在院子里撒欢。
cattle let loose to graze on the green fields
在草地上自由地吃草的牛
— often used figuratively常用作比喻
It’s the end of the school year, when schools turn students loose on our towns.
学年结束，学校放假期间学生们在我们各个镇上随意活动。
a director who’s willing to let her actors loose to interpret their roles however they see fit
愿意让她的演员们按自己认为适合的方式诠释角色的导演
We must find ways to stop the violence that has been let loose [=loosed] on the city.
如何制止城市中肆虐的暴力活动
: to produce (something, such as a cry) in a sudden and forceful way突然迸发
The crowd let loose (=let out) an enormous groan when the pass was intercepted.
传球被拦截时人群中发出了巨大的叹息声。
She let loose (with) a scream.
她突然发出一声尖叫。