sheathyoudaoicibaDictYouDict[sheath 词源字典]
sheath: [OE] A sheath is probably etymologically a ‘split stick’. The word comes from a prehistoric Germanic *skaithiz, which also produced German scheide, Dutch schede, and Danish skede. This seems to have been derived from the base *skaith ‘divide, split’ (source also of English shed ‘give off, drop’ and ski), in which case the notion underlying it would have been of a stick split open so that a sword blade could be inserted into it.
=> shed, ski[sheath etymology, sheath origin, 英语词源]
sheath (n.)youdaoicibaDictYouDict
Old English sceað, scæð, from Proto-Germanic *skaithiz (cognates: Old Saxon scethia, Old Norse skeiðir (plural), Old Frisian skethe, Middle Dutch schede, Dutch schede, Old High German skaida, German scheide "a sheath, scabbard"), according to OED, possibly from root *skei- "divide, split" (see shed (v.)) on notion of a split stick with the sword blade inserted. Meaning "condom" is recorded from 1861; sense of "close-fitting dress or skirt" is attested from 1904.