"archean" in the noun sense
1. Archean, Archean eon, Archean aeon, Archeozoic, Archaeozoic, Archeozoic eon, Archaeozoic aeon
the time from 3,800 million years to 2,500 million years ago earth's crust formed unicellular organisms are earliest forms of life
"archean" in the adjective sense
1. archean, archaean
of or relating to the earliest known rocks formed during the Precambrian Eon
Source: WordNet® (An amazing lexical database of English)
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