adj．未扣紧的，松开的：指未被固定、扣紧或锁住的状态。
v．解开，松开：指将某物从固定、扣紧或锁住的状态中释放出来。
unfasten /ʌnˈfɑːsən/ [ unfastening unfastened unfastens ]
及物动词 If you unfasten something that is closed, tied, or held together, or if you unfasten the thing holding it, you loosen or remove the thing holding it. 解开
When Ted was six we decided that he needed to know how to fasten and unfasten his seat belt.
泰德六岁时，我们决定让他知道怎样系和解他的安全带。
cause to become undone
unfasten your belt
become undone or untied
The shoelaces unfastened
解开
解开
While they both listened, the bar was unfastened, the key was turned, and the door flew open.
当他们都在听的时候，门闩被打开了，钥匙拧了拧，门被打开了。
The button on my coat came unfastened.
我大衣上的扣子脱了。
He unfastened the buttons of his shirt.
他解开了衬衣纽扣。
He sank into a black leather chair and unfastened the top button on his shirt.