οἰωνός (oiōnos)

1. a large bird, bird of prey , such as a vulture or eagle , and so distinguished from a common bird ὄρνις); (Homer), etc.
2. a bird of omen or augury , (Homer), etc.:—;the flight to (not from) the right, i. e. towards the East, was fortunate, and vice versa.
3. an omen, presage , drawn from these birds, Lat. auspicium or augurium , according as taken from seeing their flight or hearing their cry , (Iliad by Homer), etc.; δέκομαι τὸν οἰωνόν I accept the omen , hail it as favourable, (Herdotus Historicus)
commonly derivation from οἶος, —; most birds of prey being solitary, —; compare κοινωνός from κοινός (ML)