'equal-leavedness' originates from Modern English, formed by combining the adjective 'equal', the participial adjective 'leaved' (from 'leaf'), and the noun-forming suffix '-ness'.

'equal' comes via Middle English from Old French and Latin ('aequalis'); 'leaf' comes from Old English 'lēaf'. The compound 'equal-leavedness' is a Modern English formation created by compounding these elements and adding '-ness'.

Initially it meant simply 'the state of being equal-leaved'; this technical botanical sense has remained consistent in modern usage.