a close-fitting covering to protect something

The cable has a copper wire surrounded by a plastic sheath. 电缆是铜丝做的，外面包着塑料皮。

The nerves are protected by thin sheaths of fatty tissue. 神经由薄薄的脂肪鞘保护着。

a cover into which a knife or sword fits so that the blade cannot cut someone when it is not being used

He drew the knife from its jewelled leather sheath. 他把刀从镶有珠宝的皮鞘中抽出来。

a condom