'auspicious' originates from Latin, specifically the word 'auspicium'/'auspex', where 'avis' (through the prefix 'aus-') meant 'bird' and the element derived from 'specere' meant 'to look' or 'observe' (relating to taking omens from birds).

'auspicious' came into English via Late Latin and possibly Old French forms (from Latin 'auspicium' and 'auspex') and developed into Middle English forms before becoming the modern English word 'auspicious'; the adverb 'auspiciously' was later formed from the adjective.

Initially related to observing omens (especially from birds) and indicating an omen, it evolved to mean 'indicating or promising success; favorable' in general usage.