1.  A case for the reception of a sword, hunting knife, or other long and slender instrument; a scabbard. [1913 Webster]
"The dead knight's sword out of his sheath he drew." [1913 Webster]

2.  Any sheathlike covering, organ, or part. [1913 Webster]

sheath, n. (pl. sheaths)
1 a close-fitting cover, esp. for the blade of a knife or sword.
2 a condom.
3 Bot., Anat., & Zool. an enclosing case or tissue.
4 the protective covering round an electric cable.
5 a woman's close-fitting dress.

Idiom:
sheath knife a dagger-like knife carried in a sheath.

Derivative:
sheathless adj.

Etymology:
OE sc{aelig}th, sceath

N  receptacle, inclosure, recipient, receiver, reservatory, compartment, cell, cellule, follicle, hole, corner, niche, recess, nook, crypt, stall, pigeonhole, cove, oriel, cave, capsule, vesicle, cyst, pod, calyx, cancelli, utricle, bladder, pericarp, udder, stomach, paunch, venter, ventricle, crop, craw, maw, gizzard, breadbasket, mouth, pocket, pouch, fob, sheath, scabbard, socket, bag, sac, sack, saccule, wallet, cardcase, scrip, poke, knit, knapsack, haversack, sachel, satchel, reticule, budget, net, ditty bag, ditty box, housewife, hussif, saddlebags, portfolio, quiver, chest, box, coffer, caddy, case, casket, pyx, pix, caisson, desk, bureau, reliquary, trunk, portmanteau, band-box, valise, grip, grip sack, skippet, vasculum, boot, imperial, vache, cage, manger, rack, vessel, vase, bushel, barrel, canister, jar, pottle, basket, pannier, buck-basket, hopper, maund, creel, cran, crate, cradle, bassinet, wisket, whisket, jardiniere, corbeille, hamper, dosser, dorser, tray, hod, scuttle, utensil, brazier, cuspidor, spittoon, cistern, vat, caldron, barrel, cask, drum, puncheon, keg, rundlet, tun, butt, cag, firkin, kilderkin, carboy, amphora, bottle, jar, decanter, ewer, cruse, caraffe, crock, kit, canteen, flagon, demijohn, flask, flasket, stoup, noggin, vial, phial, cruet, caster, urn, epergne, salver, patella, tazza, patera, pig gin, big gin, tyg, nipperkin, pocket pistol, tub, bucket, pail, skeel, pot, tankard, jug, pitcher, mug, pipkin, galipot, gallipot, matrass, receiver, retort, alembic, bolthead, capsule, can, kettle, bowl, basin, jorum, punch bowl, cup, goblet, chalice, tumbler, glass, rummer, horn, saucepan, skillet, posnet, tureen, beaker, flask, Erlenmeyer flask, Florence flask, round-bottom flask, graduated cylinder, test tube, culture tube, pipette, Pasteur pipette, disposable pipette, syringe, vial, carboy, vacuum flask, Petri dish, microtiter tray, centrifuge tube, bail, beaker, billy, canakin, catch basin, catch drain, chatti, lota, mussuk, schooner, spider, terrine, toby, urceus, plate, platter, dish, trencher, calabash, porringer, potager, saucer, pan, crucible, glassware, tableware, vitrics, compote, gravy boat, creamer, sugar bowl, butter dish, mug, pitcher, punch bowl, chafing dish, shovel, trowel, spoon, spatula, ladle, dipper, tablespoon, watch glass, thimble, closet, commode, cupboard, cellaret, chiffonniere, locker, bin, bunker, buffet, press, clothespress, safe, sideboard, drawer, chest of drawers, chest on chest, highboy, lowboy, till, scrutoire, secretary, secretaire, davenport, bookcase, cabinet, canterbury, escritoire, etagere, vargueno, vitrine, chamber, apartment, room, cabin, office, court, hall, atrium, suite of rooms, apartment, flat, story, saloon, salon, parlor, by-room, cubicle, presence chamber, sitting room, best room, keeping room, drawing room, reception room, state room, gallery, cabinet, closet, pew, box, boudoir, adytum, sanctum, bedroom, dormitory, refectory, dining room, salle-a-manger, nursery, schoolroom, library, study, studio, billiard room, smoking room, den, stateroom, tablinum, tenement, bath room, bathroom, toilet, lavatory, powder room, john, jakes, necessary, loo, men's room, ladies' room, rest room, (uncleanness), 653 attic, loft, garret, cockloft, clerestory, cellar, vault, hold, cockpit, cubbyhole, cook house, entre-sol, mezzanine floor, ground floor, rez-de-chaussee, basement, kitchen, pantry, bawarchi-khana, scullery, offices, storeroom, lumber room, dairy, laundry, coach house, garage, hangar, outhouse, penthouse, lean-to, portico, porch, stoop, stope, veranda, patio, lanai, terrace, deck, lobby, court, courtyard, hall, vestibule, corridor, passage, breezeway, ante room, ante chamber, lounge, piazza, veranda, conservatory, greenhouse, bower, arbor, summerhouse, alcove, grotto, hermitage, lodging, bed, carriage, capsular, saccular, sacculated, recipient, ventricular, cystic, vascular, vesicular, cellular, camerated, locular, multilocular, polygastric, marsupial, siliquose, siliquous.

N  covering, cover, baldachin, baldachino, baldaquin, canopy, tilt, awning, tent, marquee, tente d'abri, umbrella, parasol, sunshade, veil (shade), shield, roof, ceiling, thatch, tile, pantile, pentile, tiling, slates, slating, leads, barrack, plafond, planchment, tiling, shed, top, lid, covercle, door, operculum, bulkhead, bandage, plaster, lint, wrapping, dossil, finger stall, coverlet, counterpane, sheet, quilt, tarpaulin, blanket, rug, drugget, housing, antimacassar, eiderdown, numdah, pillowcase, pillowslip, linoleum, saddle cloth, blanket cloth, tidy, tilpah, apishamore, integument, tegument, skin, pellicle, fleece, fell, fur, leather, shagreen, hide, pelt, peltry, cordwain, derm, robe, buffalo robe, cuticle, scarfskin, epidermis, clothing, mask, peel, crust, bark, rind, cortex, husk, shell, coat, eggshell, glume, capsule, sheath, sheathing, pod, cod, casing, case, theca, elytron, elytrum, involucrum, wrapping, wrapper, envelope, vesicle, corn husk, corn shuck, dermatology, conchology, testaceology, inunction, incrustation, superimposition, superposition, obduction, scale, veneer, facing, overlay, plate, silver plate, gold plate, copper plate, engobe, ormolu, Sheffield plate, pavement, coating, paint, varnish, plating, barrel plating, anointing, enamel, epitaxial deposition, vapor deposition, ground, whitewash, plaster, spackel, stucco, compo, cerement, ointment, covering, superimposed, overlaid, plated, cutaneous, dermal, cortical, cuticular, tegumentary, skinny, scaly, squamous, covered, imbricated, loricated, armor plated, ironclad, under cover, cowled, cucullate, dermatoid, encuirassed, hooded, squamiferous, tectiform, vaginate.

VB  invest, cover, envelope, lap, involve, inwrap, enwrap, wrap, fold up, wrap up, lap up, muffle up, overlap, sheath, swathe, swaddle, roll up in, circumvest, vest, clothe, array, dress, dight, drape, robe, enrobe, attire, apparel, accounter, rig, fit out, deck, perk, equip, harness, caparison, wear, don, put on, huddle on, slip on, mantle.

medullary sheath, myelin sheath, schwann's sheath, sheath knife, sheath pile