sheath

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A usually close-fitting case or covering for a blade, as of a sword.
• noun Any of various similar coverings.
• noun Biology An enveloping tubular structure, such as the base of a grass leaf that surrounds the stem or the tissue that encloses a muscle or nerve fiber.
• noun A close-fitting dress.
• noun A condom.

from The Century Dictionary.

• noun A case or covering, especially one which fits closely: as, the sheath of a sword. Compare scabbard.
• noun Any somewhat similar covering.
• noun In zoology, some sheathing, enveloping, or covering part.
• noun () The preputlal sheath into which the penis is retracted in many animals, as the horse, bull, dog, etc. This sheath corresponds in the main with the foreskin of man, and is often called prepuce.
• noun An elytron, wing-cover, or wing-case of an insect.
• noun The horny covering of the bill or feet of a bird; especially, a sort of false cere of some birds, as the sheathbills, jagers, etc. See cuts under puffin.
• noun The lorica or test which envelops many infusorians or other protozoans, some rotifers, etc.
• noun The fold of skin into which the claws of a cat or other feline may be retracted.
• noun In anatomy, specifically, a membrane, fascia, or other sheet or layer of condensed connective tissue which closely invests a part or organ, and serves to bind it down or hold it in place. Such sheaths may be cylindrical, as when investing a nerve or blood-vessel and extending in its course; or flat and expansive, as when binding down muscles. A layer of deep fascia commonly forms a continuous sheath of all the muscles of a limb, as notably in the case of the fascia lata, which envelops the thigh, and is made tense by a special muscle (the tensor fasciæ latæ). See fascia, 7.
• noun A structure of loose stones for confining a river within its banks.
• noun The sheath of a leaf.
• noun Specifically— The membranous toothed girdle which surrounds each node of an Equisetum, corresponding to the foliage of the higher orders of plants. See cut under Equisetum.
• noun The outer leaf becomes thickened about the middle of the internode, inclosing a nucleus.
• noun In old plows, the bar connecting the beam and sole in front: so called as sheathing the edge of the mold-board. It corresponds to the standard and in part to the shin (see shin, 8) of a modern plow. See plow, 1.
• noun The white substance of Schwann which surrounds the axis-cylinder in a nerve-fibril.
• Same as sheathe.

from the GNU version of the Collaborative International Dictionary of English.

• noun A case for the reception of a sword, hunting knife, or other long and slender instrument; a scabbard.
• noun Any sheathlike covering, organ, or part.
• noun (Bot.) The base of a leaf when sheathing or investing a stem or branch, as in grasses.
• noun (Zoöl.) One of the elytra of an insect.
• noun (Anat.) See under Medullary.
• noun (Anat.) See Neurilemma.
• noun a knife with a fixed blade, carried in a sheath.
• noun (Anat.) See Schwann's sheath.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A scabbard; a holster for a sword.
• noun Anything that has a similar shape to a scabbard for a sword that is for the purpose of holding an object that is longer than it is wide; a case.
• noun A tight-fitting dress.
• noun UK A condom.
• noun The foreskin of certain animals, e.g. dogs and horses.
• verb To put an object (especially a weapon, in particular, a sword) into its sheath.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a protective covering (as for a knife or sword)
• noun a dress suitable for formal occasions
• noun an enveloping structure or covering enclosing an animal or plant organ or part