That's a good question.

v.tr.（及物动词）
1. To undo or loosen (a knot or something knotted).
解开：解开或松开（一个绳结或纠结在一起的某物）

2 To free from something that binds or restrains:
使解脱：把…从对其束缚或限制的某个事物下解脱：
untie a horse from a tree.
把一匹马从系着的树上解下来

3 To straighten out (difficulties, for example); resolve.
解决（比如，困难）；解开

v.intr.（不及物动词）
To become untied.
被解开（或解下）



untie

vi.
解开, 松开
untie a package
解开包裹

untie *****.from his promise
使某人不再受诺言的约束

untie a difficulty
解决困难