How do you spell Sheath

Available Definitions:
1)  n. - A case for the reception of a sword, hunting knife, or other long and slender instrument; a scabbard.
2)  n. - Any sheathlike covering, organ, or part.
3)  n. - The base of a leaf when sheathing or investing a stem or branch, as in grasses.
4)  n. - One of the elytra of an insect.