sheath

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A case for a blade, as of a sword.
2. n. Any of various similar coverings.
3. n. 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.
4. n. A close-fitting dress.
5. n. A condom.
6. v. To encase or cover with or as if with a sheath; sheathe.

Century Dictionary and Cyclopedia

1. n. A case or covering, especially one which fits closely: as, the sheath of a sword. Compare scabbard.
2. n. Any somewhat similar covering. In botany, the part of an expanded organ that is rolled around a stem or other body, forming a tube, as in the lower part of the leaves of grasses, the stipules of the Polygonaceæ, the tubular organ inclosing the seta of mosses, etc.; a vagina; also, an arrangement of cells inclosing a cylindrical body, as the medullary sheath. See cuts under Equisetum, exogen, and ocrea.
3. n. In zoology, some sheathing, enveloping, or covering part.
4. n. () 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.
5. n. An elytron, wing-cover, or wing-case of an insect.
6. n. 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.
7. n. The lorica or test which envelops many infusorians or other protozoans, some rotifers, etc.
8. n. The fold of skin into which the claws of a cat or other feline may be retracted.
9. n. 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.
10. n. A structure of loose stones for confining a river within its banks.
11. n. The sheath of a leaf.
12. n. 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.
13. n. The outer leaf becomes thickened about the middle of the internode, inclosing a nucleus.
14. Same as sheathe.
15. n. 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.
16. n. The white substance of Schwann which surrounds the axis-cylinder in a nerve-fibril.

Wiktionary

1. n. A scabbard; a holster for a sword.
2. n. 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.
3. n. A tight-fitting dress.
4. n. A condom.
5. n. The skin covering the penis of e.g. a dog or a horse.
6. v. To put an object (especially a weapon, in particular, a sword) into its sheath.

GNU Webster's 1913

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.

WordNet 3.0

1. n. a protective covering (as for a knife or sword)
2. n. a dress suitable for formal occasions
3. n. an enveloping structure or covering enclosing an animal or plant organ or part