-enni-, -ennial, -ennium
(Latin: year, years)
2. A religious belief that the millennium is an era (not necessarily a literal thousand years) during which Christ will reign over the earth, not from a literal and earthly throne, but through the gradual increase of the Gospel and its power to change lives.
After this gradual Christianization of the world, Christ will return and immediately usher the church into their eternal state after judging the wicked.
This is called postmillennialism because the view is that Christ will return after the millennium.
2. The belief that Jesus Christ will return for the Last Judgment just before the one-thousand-year reign of peace.
Premillennialists place the return of Christ just before the millennium and just after a time of great apostasy and tribulation.
After the millennium, Satan will be loosed and Gog and Magog will rise against the kingdom of God; this will be immediately followed by the final judgment.
While similar in some respects to the dispensational variety; in that they hold to Christ's return being before the establishment of a thousand-year earthly reign), historical premillennialism differs in significant ways (notably in their method of interpreting Scripture.
The historical premillennialist's viewpoint interprets some prophecy in Scripture as having literal fulfillment while others demand a semi-symbolic fulfillment.
2. Lasting for fifteen years.
3. A fifteenth year of existence or duration; fifteenth anniversary.
From Latin quindecim, "fifteen" [quinque, "five" plus decem, "ten" plus -ennial, "year"].