Oikoumene (G3625) originally referred to the inhabited, civilized world โ in the Roman era, effectively the Empire. In the New Testament it carries eschatological weight: the gospel must be preached to the whole oikoumene before the end (Matthew 24:14). Satan offers Jesus all the kingdoms of the oikoumene in the temptation.
The word encodes the scope of both Satan's claim and God's redemption. Luke 2:1 uses it for Caesar's empire โ suggesting the political world-order into which the Savior of the whole oikoumene was born. Acts 17:6 records the charge against Paul's companions: 'These people who have been turning the world [oikoumene] upside down.' The gospel is inherently world-shaking.