'atrorubent' originates from Latin, specifically the word 'atrorubens', where 'atro-' meant 'dark' or 'black' and 'rubens' meant 'reddening' or 'becoming red'.

'atrorubens' from Classical/Late Latin passed into Medieval/Late scientific Latin as 'atrorubent-' and was borrowed into English (mainly in botanical and descriptive contexts) as 'atrorubent'.

Initially it meant 'becoming dark red' or 'darkly reddening'; over time it came to be used adjectivally in English to mean 'having a dark or deep red color'.