infaust
Unlucky, unfortunate, ill-omened; unpropitious; sinister.
archaic
Nevertheless, it was an infaust and sinister augury for Austin Caxton[.]
Of a prognosis: Poor, grim.
rare
Where it comes from
From Latin īnfaustus, from in- (“not”) + faustus (“fortunate, lucky”).
Adapted from the Wiktionary entry infaust (CC BY-SA 4.0).