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

bed pillow, cover slip, freudian slip, let slip, long pillow, pillow, pillow block, pillow fight, pillow lace, pillow lava, pillow sham, pillow talk, pink slip, side slip, slip, slip away, slip back, slip by, slip carriage, slip clutch, slip coach, slip friction clutch, slip in, slip noose, slip of paper, slip of the tongue, slip off, slip on, slip one's mind, slip out of, slip ring, slip road, slip stitch, slip up, throw pillow