元古宙 yuángǔzhòu Proterozoic Origin Definitions Defs Strokes Stroke Words Sentences Sents 元 yuán eon (geology) eon古 gǔ adjective ancient ancient; old; from the distant past; referring to former times as opposed to the present宙 zhòu eon (geology) the largest unit of geological time, corresponding to the chronostratigraphic unit "eonothem"