Noun
decamillennium (plural decamillennia or decamillenniums)
A period of time consisting of ten thousand years.
Coordinate terms: annum, biennium, triennium, quadrennium, quinquennium, sexennium, septennium, octennium, novennium, decennium, centennium, quincentennium, millennium, centimillennium, millionennium