'isophyllousness' originates from Greek, specifically the elements 'iso-' from 'isos' meaning 'equal' and 'phyll-' from 'phyllon' meaning 'leaf', plus the English adjectival suffix '-ous' and nominal suffix '-ness'.

'isophyllousness' formed by combining the Greek-derived combining form 'iso-' and 'phyllous' (from 'phyllon') into the English adjective 'isophyllous', which later took the nominalizing suffix '-ness' to produce 'isophyllousness'.

Initially built from roots meaning 'equal' and 'leaf', the compound retained the original literal sense and evolved into a specialized botanical term meaning 'the condition of having equally sized leaves'.