The Collaborative International Dictionary of English v.0.48:
Austral \Aus"tral\, a. [L. australis, fr. auster: cf. F.
1. Southern; lying or being in the south; as, austral land;
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.