The Collaborative International Dictionary of English v.0.48:

outback \outback\ n.
   The remote bush country of Australia; as, they hunted
   kangaroo in the outback. [Australian]
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

outback \outback\ adj.
   same as out-of-the-way. [prenominal]

   Syn: backwoods(prenominal), out-of-the-way, remote.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

outback
    adj 1: inaccessible and sparsely populated; [syn: outback(a),
           remote]
    n 1: the bush country of the interior of Australia

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "outback":
   Arabia Deserta, China, Darkest Africa, Death Valley,
   God knows where, Greenland, Lebensraum, North Pole, Outer Mongolia,
   Pago Pago, Pillars of Hercules, Sahara, Siberia, South Pole, Thule,
   Tierra del Fuego, Timbuktu, Ultima Thule, Yukon, air space,
   antipodes, back, back country, back of beyond, back-country,
   backwood, backwoods, backwoodsy, barren, barren land, barrens,
   boondock, boondocks, borderland, brush, bush, bush country,
   bushveld, clear space, clearance, clearing, desert, desolation,
   distant prospect, dust bowl, empty view, forests, frontier, glade,
   godforsaken place, heath, hinterland, howling wilderness,
   jumping-off place, karroo, living space, lunar landscape,
   lunar waste, nowhere, open country, open space, outer space,
   outpost, outskirts, plain, pole, prairie, salt flat, steppe,
   sylvan, terrain, territory, the Great Divide, the South Seas,
   the boondocks, the bush, the moon, the sticks, the tullies,
   timbers, uninhabited region, up-country, virgin, virgin land,
   virgin territory, waste, wasteland, weary waste, wide-open spaces,
   wild, wild West, wilderness, wilds, woodland, woodlands, woods