Millennium A millennium (plural: millennia) is a time period of one thousand (1000) years. The word millennium is derived from two Latin words mille ("thousand") and annum ("year"). vteMillenniaCE / AD 1st 2nd 3rd far future BCE / BC 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th prehistory natural history This short article can be made longer. You can help Wikipedia by adding to it.