'atramental' originates from Latin, specifically the word 'atramentum', where 'ater' meant 'black' and '-mentum' was a noun-forming suffix indicating means or result.

'atramentum' passed into Late Latin/Medieval Latin and then into Middle English as 'atrament' (meaning 'black ink'); from these forms the adjective 'atramental' (and related 'atramentous') appeared in Early Modern English.

Initially, it meant 'of or relating to black ink'; over time the word retained that literal sense and was also used more generally or figuratively to mean 'very dark' or 'inky'.