1.  headstone(n = noun.artifact) key, keystone - the central building block at the top of an arch or vault; Array
is a kind of building block
is a part of arch
has particulars: coign, coigne, quoin

2.  headstone(n = noun.artifact) gravestone, tombstone - a stone that is used to mark a grave; Array
is a kind of memorial, monument, stone
is a part of grave, tomb

1.  The principal stone in a foundation; the chief or corner stone. Ps. cxviii. 22. [1913 Webster]

2.  The stone at the head of a grave. [1913 Webster]

headstone, n. a (usu. inscribed) stone set up at the head of a grave.

N  support, ground, foundation, base, basis, terra firma, bearing, fulcrum, bait, caudex crib, point d'appui, pou sto, purchase footing, hold, locus standi, landing place, landing stage, stage, platform, block, rest, resting place, groundwork, substratum, riprap, sustentation, subvention, floor, supporter, aid, prop, stand, anvil, fulciment, cue rest, jigger, monkey, stay, shore, skid, rib, truss, bandage, sleeper, stirrup, stilts, shoe, sole, heel, splint, lap, bar, rod, boom, sprit, outrigger, ratlings, staff, stick, crutch, alpenstock, baton, staddle, bourdon, cowlstaff, lathi, mahlstick, post, pillar, shaft, thill, column, pilaster, pediment, pedicle, pedestal, plinth, shank, leg, socle, zocle, buttress, jamb, mullion, abutment, baluster, banister, stanchion, balustrade, headstone, upright, door post, jamb, door jamb, frame, framework, scaffold, skeleton, beam, rafter, girder, lintel, joist, travis, trave, corner stone, summer, transom, rung, round, step, sill, angle rafter, hip rafter, cantilever, modillion, crown post, king post, vertebra, columella, backbone, keystone, axle, axletree, axis, arch, mainstay, trunnion, pivot, rowlock, peg, tiebeam, thole pin, board, ledge, shelf, hob, bracket, trevet, trivet, arbor, rack, mantel, mantle piece, mantleshelf, slab, console, counter, dresser, flange, corbel, table, trestle, shoulder, perch, horse, easel, desk, clotheshorse, hatrack, retable, teapoy, seat, throne, dais, divan, musnud, chair, bench, form, stool, sofa, settee, stall, arm chair, easy chair, elbow chair, rocking chair, couch, fauteuil, woolsack, ottoman, settle, squab, bench, aparejo, faldstool, horn, long chair, long sleeve chair, morris chair, lamba chauki, lamba kursi, saddle, pannel, pillion, side saddle, pack saddle, pommel, bed, berth, pallet, tester, crib, cot, hammock, shakedown, trucklebed, cradle, litter, stretcher, bedstead, four poster, French bed, bunk, kip, palang, bedding, bichhona, mattress, paillasse, pillow, bolster, mat, rug, cushion, footstool, hassock, tabouret, tripod, monopod, Atlas, Persides, Atlantes, Caryatides, Hercules, supporting, supported, fundamental, dorsigerous, astride on, straddle.