WordNet (r) 3.0 (2006):

acres
    n 1: extensive landed property (especially in the country)
         retained by the owner for his own use; "the family owned a
         large estate on Long Island" [syn: estate, land,
         landed estate, acres, demesne]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "acres":
   abundance, alluvion, alluvium, arable land, bags, barrels, bushel,
   chattels real, clay, clod, copiousness, countlessness, crust,
   demesne, dirt, domain, dry land, dust, earth, flood, freehold,
   glebe, grassland, ground, grounds, honor, land, landed property,
   landholdings, lands, lithosphere, load, lot, lots, manor,
   marginal land, marl, mass, messuage, mold, mountain, much,
   multitude, numerousness, ocean, oceans, parcel, peck, plat,
   plenitude, plenty, plot, praedium, profusion, property, quadrat,
   quantities, quantity, real estate, real property, realty, region,
   regolith, sea, sod, soil, spate, subaerial deposit, subsoil,
   superabundance, superfluity, tenements, terra, terra firma,
   terrain, territory, the country, toft, tons, topsoil, volume,
   woodland, world, worlds