1590s, from in- (1) "not, opposite of" + auspicious. Related: Inauspiciously; inauspiciousness. The Latin word was inauspicatus "without auspices; with bad auspices," which had a brief career in English as inauspicate (17c.).
inaudibility
inaudible
inaugural
inaugurate
inauguration
inauspicious
inauthentic
in-between
inboard
inborn
inbound