flagstone(n = noun.artifact) flag - stratified stone that splits into pieces suitable as paving stones;
is a kind of paving stone

   A flat stone used in paving, or any rock which will split into such stones. See Flag, a stone. [1913 Webster]

N  layer, stratum, strata, course, bed, zone, substratum, substrata, floor, flag, stage, story, tier, slab, escarpment, table, tablet, dess, flagstone, board, plank, trencher, platter, plate, lamina, lamella, sheet, foil, wafer, scale, flake, peel, coat, pellicle, membrane, film, leaf, slice, shive, cut, rasher, shaving, integument, eschar, stratification, scaliness, nest of boxes, coats of an onion, monolayer, bilayer, trilayer, lamellar, lamellated, lamelliform, layered, laminated, laminiferous, micaceous, schistose, schistous, scaly, filmy, membranous, pellicular, flaky, squamous, foliated, foliaceous, stratified, stratiform, tabular, discoid, spathic, spathose, trilamellar, graphitic.

N  smoothness, polish, gloss, lubricity, lubrication, down, velvet, velure, silk, satin, velveteen, velour, velours, velumen, glass, ice, slide, bowling green, asphalt, wood pavement, flagstone, flags, roller, steam roller, lawn roller, rolling pin, rolling mill, sand paper, emery paper, emery cloth, sander, flat iron, sad iron, burnisher, turpentine and beeswax, polish, shoe polish, lapidary, lapidary, lapidarian, smooth, polished, leiodermatous, slick, velutinous, even, level, plane, sleek, glossy, silken, silky, lanate, downy, velvety, glabrous, slippery, glassy, lubricous, oily, soft, unwrinkled, smooth as glass, smooth as ice, smooth as monumental alabaster, smooth as velvet, smooth as oil, slippery as an eel, woolly, smooth as silk, slippery as coonshit on a pump handle, slippery as a greased pig.