Prophecy (4)
'prophecy' is the definition.
(oracle is a kind of prophecy)
This is all the clue.
(Other definitions for oracle that I've seen before include "Agency of divine revelation" , "Ancient Greek expounder of wisdom" , "Agent of divine revelation" , "Divinely-inspired prophecy" , "Augur - prediction" .)
'prophecy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for omen that I've seen before include "Auspice" , "Event regarded as a prophetic sign of good or evil" , "writing on the wall" , "Augur" , "Sign of things to come" .)