'greenfly' originates from English, specifically the compound of 'green' and 'fly', where 'green' meant the color and 'fly' meant 'flying insect'.

'green' comes from Old English 'grēne' and 'fly' comes from Old English 'flēoge' / 'flēogan'; the compound 'greenfly' has been used in English since at least the early modern period to refer to small green insects and later became commonly used for aphids.

Initially, it referred generally to small green flying insects; over time the term became specialized in common usage to refer to aphids (sap-sucking plant pests).