'epigean' originates from Greek, specifically the word 'epigeios', where 'epi-' meant 'upon' and 'gē' (ge-) meant 'earth'.

'epigeios' passed into Late Latin/Medieval Latin forms (e.g. 'epigeus') and from such classical/learned formations entered English as 'epigean' in scientific and technical usage.

Initially it meant 'upon the earth' in a literal sense, and over time it evolved into the more specific modern sense 'living on or occurring at the earth's surface'.