'racemous' originates from Latin, specifically the word 'racemus', where 'racemus' meant 'a bunch of grapes; cluster'.

'racemous' derives from Latin 'racemosus' (New Latin/Medieval Latin), formed from 'racemus' + suffix '-osus' meaning 'full of', and entered English usage as a technical botanical adjective (cf. 'racemose').

Initially it meant 'full of clusters' (in Latin), and over time it narrowed to the botanical sense 'having racemes' used in modern English.