'auspicious' originates from Latin, specifically the word 'auspicium' (related to 'auspex'), where 'avis' meant 'bird' and 'specere' meant 'to look' (so originally related to observing birds for omens).

'auspicious' changed from the Latin word 'auspicium' (and the agent noun 'auspex') into Late Latin and then entered Middle English (via ecclesiastical/learned usage), eventually becoming the modern English adjective 'auspicious' and the noun 'auspiciousness'.

Initially it referred to signs or omens (especially those from observing birds), but over time it evolved into the broader modern sense of 'indicating or conducive to success; favorable'.