h₂owi-k-
“relating to birds”avian, aviary, aviation, auspice
Extended form of *h₂éwis giving Latin avis, English avian, aviary, aviation, auspice.
Discussion
The PIE form *h₂owi-k- (relating to birds, of the bird-kind) is a relational derivative of *h₂éwis (bird — see the full treatment of the PIE bird word), formed with the suffix *-k- that creates adjectives of belonging. The meaning is "pertaining to birds" — and from this adjective, the IE languages built vocabulary for bird-watching as a form of divination.
Latin avis (bird) and the derivative auspex (avis + specere, "bird-watcher" — one who observes birds for omens) connect to this formation. The word auspice (a bird-omen) and auspicious ("of good bird-signs") preserve the Roman practice of augury — divination by watching the flight, feeding, and cries of birds. No major Roman decision was taken without consulting the auspices.
The word augur (a priest of bird-divination) may derive from a compound *awi-gus- ("bird-observer"), connecting to this adjectival root. From augur came inaugurate (to take office under favourable bird-signs) and august (consecrated by augury, hence venerable — and the month August, named for Augustus Caesar).
The root's significance extends beyond ornithology into political theology: the PIE speakers apparently believed that birds carried messages from the divine realm, and the Romans institutionalised this belief into one of their most important religious practices. The words auspicious and inaugurate preserve this ancient bird-theology in modern institutional vocabulary.