'aphid-friendly' originates from Modern English as a compound of 'aphid' + 'friendly'; 'aphid' names the insect group and 'friendly' means 'inclined toward' or 'kind to'.

'aphid' comes into English from New Latin (family name Aphididae) ultimately from Greek 'aphis' meaning 'plant louse'; 'friendly' comes from Old English 'frēondlic' (from 'frēond' = 'friend' + suffix '-lic'), passing through Middle English 'friendlich' to modern 'friendly'. The compound formation follows a common modern English pattern of noun + -friendly (e.g., 'user-friendly').

Originally 'friendly' meant 'of a friend' or 'befriending'; in compounds like 'aphid-friendly' it has come to mean 'favorable or attractive to' (i.e., 'friendly to aphids'), while 'aphid' has retained the sense of the insect group.