1.  The pin or spindle on which a wheel revolves, or which revolves with a wheel. [1913 Webster]

2.  A transverse bar or shaft connecting the opposite wheels of a car or carriage; an axletree. [1913 Webster]

3.  An axis; as, the sun's axle. [1913 Webster]
" Railway axles are called leading and trailing from their position in the front or in the rear of a car or truck respectively." [1913 Webster]
"Had from her axle torn
The steadfast earth." [1913 Webster]

axle, n. a rod or spindle (either fixed or rotating) on which a wheel or group of wheels is fixed.

Etymology:
orig. axle-tree f. ME axel-tre f. ON {ouml}xull-tr{eacute}

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.

N  rotation, revolution, spinning, gyration, turning about an axis, turning aound an axis, circulation, roll, circumrotation, circumvolution, circumgyration, volutation, circination, turbination, pirouette, convolution, verticity, whir, whirl, eddy, vortex, whirlpool, gurge, countercurrent, Maelstrom, Charybdis, Ixion, cyclone, tornado, whirlwind, dust devil, spin-out, axis, axis of rotation, swivel, pivot, pivot point, axle, spindle, pin, hinge, pole, arbor, bobbin, mandrel, axle shaft, gymbal, hub, hub of rotation, helix, helical motion, angular momentum, angular velocity, revolutions per minute, RPM, centrifugal force, surge, vertigo, dizzy round, coriolus force, carousel, merry-go-round, Ferris wheel, top, dreidel, teetotum, gyroscope, turntable, lazy suzan, screw, whirligig, rollingstone, water wheel, windmill, wheel, pulley wheel, roulette wheel, potter's wheel, pinwheel, gear, roller, flywheel, jack, caster, centrifuge, ultracentrifuge, bench centrifuge, refrigerated centrifuge, gas centrifuge, microfuge, drill, augur, oil rig, wagon wheel, wheel, tire, tyre, trochilics, whirling dervish, rotating, rotary, rotary, circumrotatory, trochilic, vertiginous, gyratory, vortical, vorticose, head over heels, round and round, like a horse in a mill.

axle bar, axle box, axle grease, axle guard, dead axle, driving axle, live axle, wheel and axle