sheath Definition

a case for a blade (as of a knife)

an investing cover or case of a plant or animal body or body part: such as

the tubular fold of skin into which the penis of many mammals is retracted

to put into or furnish with a sheath

to plunge or bury (a weapon, such as a sword) in flesh

to withdraw (a claw) into a sheath

a knife having a fixed blade and designed to be carried in a sheath

myelin sheath

the insulating covering that surrounds an axon with multiple spiral layers of myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a nerve impulse can travel along an axon —called also medullary sheath