The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
aus-
DEFINITION:
To shine. Derivatives include east, Easter, and aurora. 1a.east, from Old English ast, east (< “the direction of the sunrise”); b.ostmark, from Old High German stan, east. Both a and b from Germanic *aust-.2a.eastern, from Old English asterne, eastern; b.Ostrogoth, from Late Latin ostro-, eastern. Both a and b from Germanic *austra-.3.Easter, from Old English astre, Easter, from Germanic *austrn-, dawn. 4. Possibly in Latin auster, the south wind, formally identical to the Germanic forms in 2 and 3, but the semantics are unclear: Austro-1. 5. Probably suffixed form *auss-, dawn, also Indo-European goddess of the dawn. a.aurora, from Latin aurra, dawn; b. eo-, Eos; eosin, from Greek s, dawn. (Pokorny aes- 86.)
ast, east (< “the direction of the sunrise”); b. ostmark, from Old High German 
stan, east. Both a and b from Germanic *aust-. 2a. eastern, from Old English 
es- 86.) 
