SHEATH

[noun] [C] - a close-fitting protective coveringThe cable has a copper wire surrounded by a plastic sheath.The nerves are surrounded and protected by thin sheaths of fatty tissue.A sheath is also a container into which a knife fits closely so that the blade cannot cut someone when it is not being used.He drew the sword from its jewelled leather sheath.(UK) A sheath is also a condom.A sheath knife is a knife with a fixed blade.He suddenly attacked the doctor with a sheath knife.