means A close-fitting cover or case, especially one for the blade of a knife or sword, or by extension a snugly fitting garment or protective tube.

from From Old English 'scēath,' going back to a Germanic root tied to the idea of splitting or separating — cousin to words in Dutch ('schede') and German ('Scheide'). The thread of meaning runs through 'something split off' to 'the thing that holds a split blade,' though the exact path is shadowy. The verb 'to sheathe' (put away the sword) grew from the noun, which is why we still 'sheathe our claws.'