1. shed => sheath.
2. The notion underlying it would have been of a stick split open so that a sword blade could be inserted into it.
sheath 剑鞘,套,护套来自古英语 sceath,套,护套,来自 proto-Germanic*skaithiz,套,护套,来自 PIE*skei,切,分 开,词源同 segment,section,science.比喻用法,即两块分开的木板,剑鞘的原型。