The Collaborative International Dictionary of English v.0.48:

Austral \Aus"tral\, a. [L. australis, fr. auster: cf. F.
   austral.]
   1. Southern; lying or being in the south; as, austral land;
      austral ocean.
      [1913 Webster]

   2. (Biogeography) Designating, or pertaining to, a zone
      extending across North America between the Transition and
      Tropical zones, and including most of the United States
      and central Mexico except the mountainous parts.
      [Webster 1913 Suppl.]

   Austral signs (Astron.), the last six signs of the zodiac,
      or those south of the equator.
      [1913 Webster]