'unequal-petaled' originates from Modern English, combining the adjective 'unequal' (from prefix 'un-' + 'equal') and the noun 'petal', where 'un-' meant 'not', 'equal' traced to Latin 'aequalis' meaning 'level, even', and 'petal' comes from Greek 'petalon' meaning 'leaf' or 'thin plate'.

'petal' changed from Greek 'petalon' to New Latin 'petalum' and then into Modern English as 'petal'; 'equal' came through Old French from Latin 'aequalis' and later acquired the negative prefix 'un-' in English to form 'unequal'; these elements were combined in Modern English to form the descriptive compound 'unequal-petaled'.

Initially the roots referred to 'not equal' and 'leaf-like plate'; over time the compound came to mean specifically 'having petals that are not equal' in botanical or descriptive contexts.