Earthan UK /ˈɜː(ɹ)θən/US /ˈɝθən/ adjective1 •(nonstandard, rare) Of or from planet Earth.When, for unknown reasons, gene-splicing with Earthan reptiles had failed to take, scientists had turned to the sea dragons found on the water world of Aquatilis, home planet of the merpeople. — 2008 formsmore Earthan · most Earthan