sheath (n.) Look up sheath at Dictionary.com
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.