1. (noun)Hadean, Hadean time, Hadean eon, Hadean aeon, Priscoan, Priscoan eon, Priscoan aeon the earliest eon in the history of the Earth from the firstaccretion of planetary material (around 4,600 millionyears ago) until the date of the oldest known rocks (about 3,800 millionyears ago); no evidence of life