The phrase "outer sheath" refers to a protective covering or layer that surrounds or encloses something. It shields or encases an object, providing an extra layer of protection. Full definition
It is a way for him to remove the dead outer sheaths of his nail, keeping it sharp all the time. (catoverdose.com)
First, it removes the dead outer sheaths of the nails, keeping the claws sharp and ready for action. (littlebigcat.com)
TINY TOMATILLO A 52 - million - year - old fossil of a tomatillo includes the plant's papery outer sheath, and remnants of the blackened berry, which has since turned to coal. (sciencenews.org)