Added 10 October 2026 archean noun Categories: TimeRare Words noun ! Definition from WordNet 3.1, Princeton University. More about archean at Wordnik → Where our words come from → The time from 3,800 million years to 2,500 million years ago; earth's crust formed; unicellular organisms are earliest forms of life. adjective Of or relating to the earliest known rocks formed during the Precambrian Eon. Related Words: archaeanearlyarchaeacratonsazoichominineproterozoicaccretionaryprimaevalnonheritablealkalicmomentaneous Back to today's word