approach, arbor, asymptote, axis, axle-tree, axle, axle bar, axle shaft, axle spindle, bottleneck, center, center of action, center of gravity, centroid, centrum, chimney, chimney corner, collision course, concentralization, concentration, concourse, concurrence, confluence, conflux, congress, convergence, converging, core, crossing, dead center, distaff, epicenter, fender, fire screen, fireboard, fireguard, fireplace, fireside, flue, focal point, focalization, focus, fulcrum, funnel, gimbal, gudgeon, heart, hearth, hearthstone, hinge, hingle, hob, ingle, inglenook, ingleside, kernel, mandrel, marrow, medulla, meeting, metacenter, middle, mutual approach, narrowing gap, nave, navel, nerve, nub, nucleus, oarlock, omphalos, pin, pintle, pith, pivot, pole, radiant, radius, rowlock, seat, smokehole, spindle, spokes, storm center, swivel, tangent, trunnion, umbilicus