pillowcase(n = noun.artifact) case, pillow slip, slip - bed linen consisting of a cover for a pillow; "the burglar carried his loot in a pillowcase"
is a kind of bed linen

   A removable case or covering for a pillow, usually of white linen or cotton cloth. [1913 Webster]

pillowcase, n. a washable cotton etc. cover for a pillow.

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.