1590s, "one who observes flights of birds for the purpose of taking omens," from Latin auspex "interpreter of omens given by birds," from PIE *awi-spek- "observer of birds," from *awi- "bird" (see aviary) + *spek- "to see" (see scope (n.1)). Compare Greek oionos "bird of prey," also "bird of omen, omen," and ornis "bird," which also could mean "omen."
